Bisphenol A and Aromatic Glycidyl Ether-Free Coatings

ABSTRACT

Disclosed are Bisphenol A (BPA), Bisphenol F, Bisphenol A diglycidyl ether (BADGE), and Bisphenol F diglycidyl ether (BFDGE)-free coating compositions for metal substrates including an under-coat composition containing a polyester (co)polymer, and an under-coat cross-linker; and an over-coat composition containing a poly(vinyl chloride) (co)polymer dispersed in a substantially nonaqueous carrier liquid, an over-coat cross-linker, and a functional (meth)acrylic (co)polymer. Also provided is a method of coating a metal substrate using the BPA, BPF, BADGE and BFDGE-free coating system to produce a hardened protective coating useful in fabricating metal storage containers. The coated substrate is particularly useful in fabricating multi-part foodstuffs storage containers with “easy-open” end closures.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of Provisional Application No.60/707,494 filed on Aug. 11, 2005 by Mayr, et al., and entitled“Bisphenol A and Aromatic Glycidyl Ether-Free Coatings,” which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The invention relates to protective coating compositions and methods forcoating metal substrates useful in fabricating, for example, packagingcontainers. The invention also relates to foodstuffs packagingcontainers, particularly multi-part containers with “easy-open” endclosures, having an interior surface coated with such protectivecoatings.

BACKGROUND

Protective coatings are applied to the interior of metal food andbeverage containers (e.g. cans) to prevent the contents from coming intocontact with the metal surfaces of the containers. Contact of thecontainer contents with the interior metal surface, especially whereacidic products such as soft drinks and tomato juice are involved, canlead to corrosion of the metal container and result in contamination anddeterioration of the contents. Protective coatings are also applied tothe interior of food and beverage containers to prevent corrosion in theheadspace of the container between the fill line of the food product andthe container lid, which is particularly problematic with high saltcontent food products.

Metal container interiors are typically coated with a thin thermosetfilm to protect the interior metal surface from its contents. Varioussynthetic (co)polymer compositions and their blends, includingpoly(vinyl chloride) (co)polymers; vinyl-functional (meth)acrylic(co)polymers; polybutadiene (co)polymers; phenol-formaldehyde(co)polymers; epoxy-functional (co)polymers; alkyd/aminoplast resins andoleoresinous materials; have been used as interior can protectivecoatings. These heat-curable (co)polymer compositions are usuallyapplied as solutions or dispersions in volatile organic solvents.

The heat-cured protective coating compositions generally should exhibitsufficient adhesion and flexibility to maintain film integrity duringcontainer fabrication. Sufficient coating adhesion and flexibility alsoare needed for the coating composition to withstand processingconditions the container is subject to during product packaging. Otherdesired performance features of the cured coatings include corrosionprotection and sufficient chemical, abrasion and mar resistance. Thecoatings used on the interior of metal food containers preferably alsomeet government regulatory criteria. For food contact, the (co)polymericand materials used in these coatings are typically derived fromcomponents acceptable to the U.S. Food and Drug Administration (FDA) aspublished in Title 21 of the Code of Federal Regulations, §175.300.

Multi-coat coating systems recently have been used to coat the interiorof food and beverage containers, wherein the over-coat or lacquercontains an epoxy resin cross-linked with a phenolic resin. Suchepoxy-based “Gold lacquers” typically exhibit good adhesion and aresuitable for storing acidic foodstuffs and beverages. However, there isa perception that some epoxy-based coatings, containing mobile BisphenolA (BPA), Bisphenol F (BPF), and aromatic glycidyl ether compounds, areless acceptable for foodstuffs storage.

Currently, the food packaging industry and consumer groups are seekingcoated metal packaging articles prepared from coating compositions freefrom mobile BPA, BPF, and aromatic glycidyl ether compounds andexhibiting excellent corrosion and chemical resistance, acceptableadhesion and flexibility during container fabrication. The art continuesto seek an ideal coating composition for use as a protective coating formetal foodstuffs containers.

SUMMARY OF THE INVENTION

The present invention is directed to hardenable, BPA, BPF, BADGE andBFDGE-free protective coating compositions for coating metal substrates.The present invention is also directed to protective coatingcompositions substantially free of mobile BPA, BPF and aromatic glycidylether compounds [e.g. Bisphenol A diglycidyl ether (BADGE), Bisphenol Fdiglycidyl ether (BFDGE) and optionally, Novolac glycidyl ether (NOGE)].

The present invention is also directed to methods useful in applyingprotective coatings to the interior lining of metal containers suitablefor contact with foodstuffs. For example, an exemplary cured coatingcomposition of the present invention demonstrates adequate chemical andphysical properties for use as a protective coating system on theinterior of metal containers used in packaging foods and beverages. Thepresent invention is further directed to a metal storage container forfoodstuffs in which the BPA, BPF,

BADGE and BFDGE-free multi-coat protective coating composition isapplied to an interior surface of the container.

One aspect of the present invention provides a hardenable packagingcoating composition comprising an under-coat composition containing apolyester (co)polymer and an under-coat cross-linker; and an over-coatcomposition containing a poly(vinyl chloride) (co)polymer dispersed in asubstantially nonaqueous over-coat carrier liquid, an over-coatcross-linker, and a functional (meth)acrylic (co)polymer; wherein thepackaging coating composition is substantially free of mobile BPA, BPF,BADGE and BFDGE. In a presently preferred embodiment, the over-coatcomposition is completely free of BPA, BPF, BADGE and BFDGE.

In certain presently preferred embodiments, the under-coat cross-linkerand/or over-coat cross-linker contain two or more functional groupsselected from hydroxyl, amino, vinyl and blocked-isocyanate. Inadditional presently preferred embodiments, the functional (meth)acrylic(co)polymer contains one or more functional groups selected fromhydroxyl, carboxyl, and oxirane. In a particularly preferred embodiment,at least one of the under-coat and over-coat compositions contains atleast one of a PVC stabilizer or a pigment.

In another aspect, the present invention provides a method for coating ametal substrate with a hardenable multi-coat packaging compositionwherein the hardened packaging composition is substantially free ofmobile BPA, BPF, BADGE and BFDGE. The method includes the steps ofapplying an under-coat composition to a metal substrate, the under-coatcomposition containing a polyester (co)polymer and an under-coatcross-linker; applying an over-coat composition to the under-coatedmetal substrate, the over-coat composition containing a poly(vinylchloride) (co)polymer dispersed in a substantially nonaqueous over-coatcarrier liquid, an over-coat cross-linker and a functional (meth)acrylic(co)polymer; and curing the under-coat and over-coat compositions toprovide a hardened film of the under-coat and over-coat composition onthe metal substrate; wherein the hardened film is substantially free ofmobile BPA, BPF, BADGE and BFDGE.

In another aspect of the present invention, a metal foodstuffs containeris provided, wherein at least an interior surface of the container iscoated with a hardened packaging coating composition according to thepresent invention. Preferably the metal foodstuffs container is amulti-part can having at least one easy-open end closure with at leastan interior surface of the easy-open end closure coated with a hardenedpackaging coating composition according to the present invention.

The hardened packaging coating composition preferably maintains metalcorrosion inhibition, imparts chemical resistance to acidic foodstuffsexposure, and achieves cured film integrity with good metal substrateand inter-coat adhesion and flexibility sufficient for containerfabrication. In certain preferred embodiments, the hardened coatingcomposition also stabilizes PVC-based organosols with respect todehydrochlorination and/or scavenges hydrochloric acid, and is thususeful in providing improved resistance to acidic foodstuffs and infabricating containers with “easy-open” end closures.

The details of one or more embodiments of the invention are set forth inthe following Detailed Description of the Preferred Embodiments. Theseand other aspects, features and advantages of the present invention willbecome apparent from the Examples and the Claims, which followthereafter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS DEFINITIONS

As used herein, the term “aromatic glycidyl ether compounds” denotescompounds selected from the group consisting of Bisphenol A diglycidylether (BADGE) [2,2′-bis(4-hydroxyphenyl)propanebis(2,3-epoxypropyl)ether], Bisphenol F diglycidyl ether (BFDGE), andNovolac glycidyl ether (NOGE), and combinations thereof, in both theuncured and cured state.

The term “substantially free” of a particular mobile compound means thatthe compositions of the present invention contain less than 100 partsper million (ppm) of the recited mobile compound.

The term “essentially free” of a particular mobile compound means thatthe composition of the present invention contains less than five partsper million of the recited mobile compound.

The term “completely free” of a particular mobile compound means thatthe compositions of the present invention contain less than 20 parts perbillion (ppb) of the recited mobile compound.

The term “mobile” means that the compound can be extracted from thecured coating when a coating (typically approximately 1 mg/cm² thick) isexposed to a ten weight percent ethanol solution for two hours at 121°C. followed by exposure for 10 days in the solution at 49° C.

If the aforementioned phrases are used without the term “mobile” (e.g.,“substantially free of BPA, BPF, BADGE and BFDGE”) then the compositionsof the present invention contain less than the aforementioned amount ofthe compound whether the compound is mobile in the coating or bound to aconstituent of the coating.

As used herein, the term “multi-coat coating system” is defined as acoating system requiring the application of at least two chemicallydistinct coating compositions to a particular substrate surface.

The term “two-coat coating system” is defined as a multi-coat coatingsystem in which only two chemically distinct coating compositions areapplied to a particular substrate surface.

The term “under-coat composition” is defined as the coating compositionto be applied between a surface of a substrate and an “over-coatcomposition,” and is synonymous with base-coat, primer or size for atwo-coat system.

The term “over-coat composition” is defined as the coating compositionto be applied over an applied under-coat composition, and is synonymouswith top-coat or lacquer for a two-coat coating system.

The term “cured coating composition” is defined as the adherent(co)polymeric coating residing on a substrate resulting from at leastpartially curing or hardening a coating composition, for example, byfilm formation, cross-linking, and the like.

The term “coating solids” is defined as including all non-volatilematerials that remain in the “cured coating composition” on the coatedsubstrate after curing.

The term “(co)polymer” is defined as a macromolecular homopolymerderived from a single reactive entity (e.g. monomer) or a macromolecularcopolymer derived from multiple reactive entities, or mixtures thereof.

Unless otherwise indicated, a reference to a “(meth)acrylate” compound(where “meth” is bracketed) is meant to include both acrylate andmethacrylate compounds.

The term “dispersed in” with respect to a polymer “dispersed in” acarrier liquid means that the polymer can be mixed into a carrier liquidto form a macroscopically uniform, multiphase (e.g. solid/liquid) fluidmixture, and is intended to include mixtures wherein the carrier liquidsolvates, swells or partially-solubilizes the dispersed polymer.

The term “substantially nonaqueous carrier liquid” is used to denote acarrier liquid in which water, if present at all, constitutes less thanabout five percent by weight of the carrier liquid.

The term “cross-linker” is used to denote a chemical compound containingtwo or more chemical groups (e.g. hydroxyl, carboxyl, vinyl and blockedisocyanate) capable of undergoing inter- or intra-molecular chemicalreaction.

The term “functional (meth)acrylic (co)polymer” is used to denote a(meth)acrylic (co)polymer containing one or more polar chemical groupsselected from hydroxyl, carboxyl and oxirane.

Coating Compositions

The present invention relates to hardenable coating compositions andprotective coating systems for metal substrates including an under-coatcomposition containing (1) a polyester (co)polymer and an under-coatcross-linker and (2) an over-coat composition containing a poly(vinylchloride) (co)polymer dispersed in a substantially nonaqueous carrierliquid, an over-coat cross-linker and a functional (meth)acrylic(co)polymer.

The hardenable coating compositions are preferably substantially free ofmobile BPA, BPF, BADGE and BFDGE. More preferably, the coatingcompositions are essentially free of mobile BPA, BPF, BADGE and BFDGE.Most preferably, the coating compositions are completely free of BPA,BPF, BADGE and BFDGE. In presently preferred embodiments, the under-coatcomposition further contains a substantially nonaqueous under-coatcarrier liquid, which need not be compositionally identical to thesubstantially nonaqueous over-coat carrier liquid.

Preferably, the polyester (co)polymer exhibits a hydroxyl number fromabout one to about 40 mg KOH per gram of polyester, and exhibits a glasstransition temperature greater than about 50° C. Preferably theunder-coat cross-linker and/or over-coat cross-linker is an aminoplastcross-linker containing at least two amino functional groups, aphenoloplast cross-linker containing at least two hydroxyl groups, ablocked-isocyanate cross-linker containing at least two blockedisocyanate groups, or a combination therof. Preferably the functional(meth)acrylic (co)polymer contains at least one functional groupselected from carboxyl, hydroxyl and oxirane.

The multi-coat metal substrate protective coating compositions of thepresent invention are suitable for use as protective surface coatings infabricating metal packages of tinplate, aluminum and tin-free steel. Themulti-coat coating systems are suitable for both the interior andexterior coating of three-piece and deep-drawn metal foodstuffcontainers, but are particularly preferred for interior coating offoodstuff containers, where the coating contacts the foodstuff.

Also provided is a method of coating a metal substrate wherein thecoating composition is substantially free of mobile BPA, BPF, BADGE andBFDGE. In presently preferred embodiments, a method of coating a metalsubstrate wherein the coating composition is completely free of BPA,BPF, BADGE, BFDGE and NOGE is provided. Further provided is a metalfoodstuffs storage container derived from a metal substrate having atleast one surface substantially coated with the hardened coatingcomposition that is substantially free of mobile BPA, BPF, BADGE andBFDGE. The composite material is particularly useful in fabricatingmetal foodstuffs storage containers, including multi-part containershaving “easy-open” end closures, wherein the hardened protective coatingcontacts the foodstuffs.

As described herein, the BPA, BPF, BADGE and BFDGE-free coatingcomposition preferably includes an under-coat composition containing apolyester (co)polymer and an under-coat cross-linker capable ofundergoing chemical cross-linking, preferably with the polyester(co)polymer.

The under-coat (i.e. base-coat, primer or size) coating compositionpreferably contains a polyester (co)polymer. A single polyester(co)polymer or a mixture of polyester (co)polymers may be used accordingto the present invention. The polyester (co)polymer or mixture of(co)polymers is preferably present in the under-coat coating compositionin an amount from about 20 to about 99 percent, and more preferablyabout 60 to about 90 percent, by weight on a non-volatile solids basis.

The chemical composition of the polyester (co)polymer is not especiallylimited. However, it is preferred that the polyester (co)polymer beterminated at each end with a functional group. One skilled in the artunderstands that typical polyester terminal groups (e.g. hydroxyl orcarboxyl groups) may, for example, be chemically reacted or exchanged toproduce terminal amino-functional, amido-functional, or urea-polyester(co)polymers using conventional chemical synthesis methods known in theart.

Preferably, the functional groups are chemically identical and areselected to be terminal hydroxyl or terminal carboxyl groups. Thefunctional groups of the polyester (co)polymer are more preferablyselected to be hydroxyl groups. The polyester (co)polymer is mostpreferably selected to exhibit a hydroxyl number from about one to about40 mg KOH per gram of polyester (co)polymer on a non-volatile solidsbasis.

Preferably the polyester (co)polymer is a macromolecule exhibiting anumber average molecular weight (M_(w))from about 500 to about 10,000Daltons, more preferably from about 1,000 to about 7,500 Da, and mostpreferably from about 3,000 to about 5,000 Da. The polyester (co)polymerpreferably exhibits a glass transition temperature (T_(g)) greater thanabout 50° C., and more preferably greater than about 60° C. Preferably,the polyester (co)polymer exhibits a T_(g) less than about 100° C., andmore preferably less than about 90° C.

The polyester (co)polymer is typically prepared by condensation(esterification) according to known processes [see, for example, ZenoWicks, Jr., Frank N. Jones and S. Peter Pappas, Organic Coatings:Science and Technology, Vol. 1, pp. 122-132 (John Wiley & Sons: NewYork, 1992)]. The polyester (co)polymer is usually derived from amixture of at least one poly-functional alcohol (polyol) (generally adihydroxy or trihydroxy alcohol) esterified with excess equivalents of amixture of at least one dicarboxylic acid or anhydride (generally anaromatic dicarboxylic acid or anhydride).

The polyester (co)polymer is typically prepared from an aromatic oraliphatic polycarboxylic acid or anhydride, and an aromatic or aliphaticdiol, triol, or polyol. The diol, polycarboxylic acid and/or anhydrideare combined in suitable proportions and chemically reacted usingstandard esterification (condensation) procedures to provide a polyesterhaving functional groups at the terminal ends of the polyester(co)polymer, which are preferably hydroxyl or carboxyl groups. Hydroxylgroups can be positioned at the terminal end of the polyester byutilizing excess diol, triol, or polyol in the reaction. A triol orpolyol is used to provide a branched, as opposed to linear, polyester.

Examples of suitable polycarboxylic acids or anhydrides include, but arenot limited to, maleic anhydride, maleic acid, fumaric acid, succinicanhydride, succinic acid, adipic acid, phthalic acid, phthalicanhydride, 5-terz-butyl isophthatic acid, tetrahydrophthalic anhydride,hexahydrophthalic anhydride, endomethylenetetrahydrophthalic anhydride,azelaic acid, sebacic acid, tetrachloro-phthalic anhydride, chlorendicacid, isophthalic acid, trimellitic anhydride, terephthalic acid, anaphthalene dicarboxylic acid, cyclohexane-dicarboxylic acid, glutaricacid, anhydrides and acids thereof, and mixtures thereof. It is alsounderstood that an esterifiable derivative of a polycarboxylic acid,such as a dimethyl ester or anhydride of a polycarboxylic acid, can beused to prepare the polyester.

Customarily, dicarboxylic acids and their esterifiable derivatives areused. Examples of such compounds include phthalic acid, isophthalicacid, terephthalic acid, 1,4-cyclohexanedicarboxylic acid, succinicacid, sebacic acid, methyltetrahydrophthalic acid,methylhexahydrophthalic acid, tetrahydrophthalic acid, dodecanedioicacid, adipic acid, azelaic acid, naphthalenedicarboxylic acid,pyromellitic acid and/or dimer fatty acids, acid anhydrides thereofand/or lower alkyl esters, for example methyl esters. Tri-carboxylicacids (e.g. trimellitic acid) may also be used.

Preferred polycarboxylic acids and their esterifiable derivativescontain aromatic functionality. Examples of preferred aromaticdicarboxylic acids are phthalic acid, terephthalic acid, isophthalicacid and dimer fatty acid; trimellitic acid is a preferred aromatictricarboxylic acid. Particularly preferred are terephthalic andisophthalic acid. The anhydride derivatives of these acids can also beused if they exist as anhydrides.

Preferably less than 10% by weight of the dicarboxylic acid contentcomprises other aliphatic polyfunctional carboxylic acids. Examples ofother aliphatic polyfunctional carboxylic acids are malonic acid,succinic acid, glutaric acid, adipic acid, azelaic acid, suberic acid,sebacic acid, dimer fatty acids, maleic acid and dimer fatty acids.Hydroxy acids can also be included in the polyester such as, forexample, 12-hydroxy stearic acid, lactic acid and 2-hydroxy butanoicacid.

Examples of suitable diols, triols, and polyols include, but are notlimited to, ethylene glycol, propylene glyco,1,3-propanediol, glycerol,diethylene glycol, dipropylene glycol, triethylene glycol,trimethylolpropane, trimethylolethane, tripropylene glycol, neopentylglycol, pentaerythritol, 1,4-butanediol, trimethylol propane, hexyleneglycol, cyclohexanedimethanol, a polyethylene or polypropylene glycolhaving a weight average molecular weight (M_(w)) of about 500 Da orless, isopropylidene bis (p-phenylene-oxypropanol-2), and mixturesthereof.

The polyol mixture may include at least one tri-hydroxy alcohol (e.g.triol), but is predominantly composed of one or more di-hydroxy alcohol(e.g. glycol or diol). Suitable tri-hydroxy alcohols include, forexample, trimethylolethane, trimethylopropane, pentaerythritol,dipentaerythritol, glycerol, and mixtures thereof. Preferred triols aretrimethylolethane and trimethylopropane. Suitable di-hydroxy alcoholsinclude, for example, ethylene glycol, propylene glycol, 1,2- and/or1,3-propanediol, diethylene glycol, dipropylene glycol, triethyleneglycol, tetraethylene glycol, 1,4-butanediol, 1,3-butylethylpropanediol,2-methyl-1,3-propanediol, 1,5-pentanediol, cyclohexanedimethanol,glycerol, 1,6-hexanediol, neopentyl glycol, pentaerythritol,trimethylolethane, trimethylolpropane, 1,4-benzyldimethanol and-ethanol, 2,4-dimethyl-2-ethylhexane-1,3-diol, and mixtures thereof.Most preferred are diols. Examples of preferred diols include ethyleneglycol, propylene glycol, diethylene glycol, neopentyl glycol, andmixtures thereof.

As noted above, the polyester (co)polymer is preferablycarboxyl-terminated or hydroxy-terminated, depending upon thestoichiometry of the esterification reaction mixture. To provide ahydroxy-terminated polyester, the equivalent excess of polyol overdicarboxylic acid should preferably be maintained from about 0.02 toabout 0.784 on a molar basis, and more preferably from about 0.04 toabout 0.554 on a molar basis. Similarly, to provide acarboxyl-terminated polyester, it is usually preferable to use atwo-step process. First, one prepares a hydroxy-polyester, and thenreacts the terminal hydroxyl groups with a molar excess of dicarboxylicacid. The equivalent excess of dicarboxylic acid over polyol generallyshould be maintained from about 0.02 to about 0.784 on a molar basis,and preferably from about 0.04 to about 0.554 on a molar basis. A modestamount (e.g. 1-5 percent by weight) of a tri-functional monomer (e.g.trimellitic anhydride) may be added to increase the number averagecarboxyl-functionality of the polyester (co)polymer.

Preferably, the polyester (co)polymer is hydroxy-terminated. In someembodiments, the hydroxyl number of the hydroxy-polyester (co)polymerranges typically from about one to about 50 milligrams KOH/g(co)polymer, and preferably from about one to about 20 mg KOH/g(co)polymer. Alternatively, the polyester (co)polymer iscarboxyl-terminated. The carboxyl-terminated polyesters typicallyexhibit an acid number (AN) of about one to about 50 mg KOH/g(co)polymer, and preferably from about one to about 20 mg KOH/g(co)polymer. Acid number may be determined using the titrimetric methoddescribed in ISO Standard XP-000892989. Hydroxyl number may bedetermined using the same standard test method, substituting a solutionof hydrochloric acid in ethanol for the potassium hydroxide in ethanoltitrant, and expressing the neutralization endpoint equivalents ofhydrochloric acid in terms of the molar equivalents of potassiumhydroxide.

Various commercially available polyester (co)polymers are suitable foruse in the present invention. For example, VITEL® polyester (co)polymers(e.g. VITEL® PE-100 and PE-200 saturated polyester (co)polymersavailable from Goodyear Tire & Rubber Co., Akron, Ohio), URALAC™polyester (co)polymers (e.g. URALAC ZW5000SH™ available from DSM ResinsU.S., Inc., Augusta, Ga.), and Dynapol™ polyester (co)polymers (e.g.Dynapol™ L and LH saturated polyester resins available from Degussa,Corp., Parsippany, N.J.). Alternatively, polyester (co)polymers may bechemically synthesized using esterification-condensation methods knownto those skilled in the art as previously described.

In preferred embodiments, the under-coat coating composition contains anunder-coat cross-linker, preferably at from about 5 to about 30 percentby weight and more preferably from about 15 to about 25 percent byweight of the under-coat composition on a non-volatile solids basis(i.e. excluding optional solvents or carrier liquids). The under-coatcross-linker preferably contains two or more functional groups capableof undergoing chemical reaction with one or more of the polyester(co)polymer, the over-coat cross-linker, and/or the functional(meth)acrylic (co)polymer.

The choice of particular under-coat cross-linker typically depends onthe particular product being formulated. For example, some coatingcompositions are highly colored (e.g., gold-colored coatings). Thesecoatings may typically be formulated using cross-linkers that themselvestend to have a yellowish color. In contrast, white or clear coatings aregenerally formulated using non-yellowing cross-linkers, or only a smallamount of a yellowing cross-linker. Preferred under-coat cross-linkersare at least substantially free of mobile BPA, BPF, BADGE and BFDGE.

The cross-linker may be any suitable compound including, for example, asingle molecule, a dimer, an oligomer, a (co)polymer or a mixturethereof. Preferably, the cross-linker is a polymeric material and morepreferably a (co)polymer. Any suitable amino-, hydroxyl-, vinyl- orisocyanate-functional cross-linkable (co)polymers can be used. Forexample, aminoplast and phenoplast (i.e. phenolic) cross-linkable(co)polymers, containing two or more active hydrogen (e.g. amino orhydroxyl) groups may be used. Alternatively, blocked isocyanatecross-linkers containing two or more blocked isocyanate groups, or anisocyanate group and a vinyl group, can be used in the under-coat.

Examples of cross-linkable aminoplast (co)polymers include thecondensation products of aldehydes such as formaldehyde, acetaldehyde,crotonaldehyde, and benzaldehyde with amino- or amido-group-containingsubstances such as urea, melamine and benzoguanamine. Examples ofsuitable cross-linking aminoplast (co)polymers include, withoutlimitation, (co)polymers containing two or more amino functional groups.Suitable aminoplast (co)polymer cross-linkers are commerciallyavailable, and include benzoguanamine-formaldehyde (co)polymers,melamine-formaldehyde (co)polymers, esterified melamine-formaldehyde(co)polymers, and urea-formadehyde (co)polymers. One specific example ofa useful aminoplast cross-linker is the fully alkylatedmelamine-formaldehyde (co)polymer commercially available from CytecIndustries (Cytec Industries GMBH, Neuss, Germany) under the trade nameof CYMEL 303.

Examples of cross-linkable phenoplast (co)polymers include thecondensation products of aldehydes with phenols. Formaldehyde andacetaldehyde are preferred aldehydes. Various phenols can be employedsuch as phenol, cresol, p-phenylphenol, p-tert-butylphenol,p-tert-amylphenol, and cyclopentylphenol. Examples of suitablecross-linking phenoplast (i.e. phenolic) (co)polymers include(co)polymers containing two or more hydroxyl functional groups thatpreferably are substantially free of mobile BPA, BPF, BADGE and BFDGE.

Phenolic cross-linkers of the resole type may be used such as, forexample, phenol, butylphenol, xylenol- and cresol-formaldehyde types,with the types specifically etherified with butanol being preferred forprotective container coatings [see, for example, Zeno Wicks, Jr., FrankN. Jones and S. Peter Pappas, Organic Coatings: Science and Technology,Vol. 1, pp. 184-186 (John Wiley & Sons: New York, 1992)].

Suitable phenolic cross-linkers are commercially available. Examples ofcommercially available phenolic cross-linkers include those known by thetradenames DUREZ™ and VARCUM™ from DUREZ Corp. (Dallas, Tex.) orReichhold Chemical AG (Austria); (CO)POLYMEROX™ from Monsanto ChemicalCo. (St. Louis, Mo.); AROFENE™ and AROTAP™ from Ashland Chemical Co.(Dublin, Ohio); and BAKELITE™ from Bakelite A.G. (Iserlohn, Germany).Particularly preferred resole phenolic cross-linkers are BAKELITE PF6470 LB™, BAKELITE 9989LB™, and VARCUM 2227 B 55™. Most preferably, oneof the two particularly preferred BAKELITE™ phenolic resins may be usedas a mixture in the under-coat coating composition with VARCUM 2227 B55, generally at a weight ratio of between 1/3 to 3/1 of BAKELITE™ toVARCUM™ phenolic cross-linker.

In certain preferred embodiments, the under-coat cross-linker isselected to be a blocked isocyanate having two or more isocyanatefunctional groups, or an isocyanate group and a vinyl group, capable ofcross-linking with at least one component of the coating composition.Preferably, the blocked isocyanate is an aliphatic and/or cycloaliphaticblocked polyisocyanate such as, for example, HDI (hexamethylenediisocyanate), IPDI (isophorone diisocyanate), TMXDI(bis[4-isocyanatocyclohexyl] methane), H₁₂MDI (tetramethylene-m-xylidenediisocyanate), TMI (isopropenyldimethyl-benzylisocyanate), dimers ortrimers thereof, and combinations thereof. Preferred blocking agentsinclude, for example, n-butanone oxime, ε-caprolactam, diethyl malonate,and secondary amines.

Suitable commercially available blocked isocyanate cross-linkersinclude, for example, VESTANAT™ B 1358 A, VESTANAT™ EP B 1186 A,VESTANAT™ EP B 1299 SV (all available from Degussa Corp., Marl, Germany)and DESMODUR™ BL 3175 (available from Bayer A.G., Leverkusen, Germany).

As described herein, the inventive coating composition preferablyincludes an over-coat composition containing a poly(vinyl chloride)(co)polymer dispersed in a substantially nonaqueous over-coat carrierliquid, an over-coat cross-linker, and a functional (meth)acrylic(co)polymer.

In preferred embodiments, the over-coat composition comprises apoly(vinyl chloride) (co)polymer dispersed in a substantially nonaqueouscarrier liquid to form an organosol. A PVC organosol is a dispersion offinely divided PVC (co)polymer particles dispersed in a carrier liquidpreferably chosen so as to dissolve the PVC (co)polymer to only a minorextent or not at all. Useful PVC (co)polymer may be in the form offinely divided polyvinyl chloride (co)polymer powder commerciallyavailable from a number of sources. In some embodiments, the PVC(co)polymer powder exhibits a volume average particle diameter of fromabout 0.5 to about 30 micrometers.

Suitable commercially available PVC (co)polymer powders include, forexample, Geon™ (available from PolyOne Corp., Pasadena, Tex.) and Vinnol(available from Wacker Chemie; Munich, Germany) poly(vinyl chloride)homopolymers and poly(vinyl chloride)-co-poly(vinyl acetate)(co)polymers. Preferably, the PVC powder is a PVC homopolymer such asGeon 171™ or Geon 178™ (available from PolyOne Corp., Pasadena, Tex.).

Preferred over-coat coating compositions comprise from about 40 to about90 percent by weight, and more preferably from about 60 to about 85percent by weight of PVC, based on the total non-volatile weight of theover-coat coating composition. The PVC is preferably added to theover-coat coating composition by what is known as a media grinding ormilling process using a ball mill, bead mill, sand mill or other similarmedia mill.

The over-coat coating composition preferably includes an over-coatcarrier liquid to effectively deliver the PVC (co)polymer powderdispersion to the substrate. The over-coat carrier liquid is preferablysubstantially nonaqueous. It should be understood that a substantiallynonaqueous coating composition can include a relatively low amount ofwater, such as up to about five percent by total weight of the over-coatcoating composition, without adversely affecting the metalcorrosion-inhibiting properties of the over-coat coating composition,either prior to or after curing. The water can be added to thecomposition intentionally, or can be present in the compositioninadvertently, such as when water is present in a particular componentincluded in the coating composition.

Substantially nonaqueous organic solvents or organic solvent blends maybe used advantageously as the over-coat carrier liquid, for example, toobtain more favorable coating rheology, to achieve faster drying or curetimes, or to effectively dissolve or solvate another component of theover-coat composition (e.g. the over-coat cross-linker or the functional(meth)acrylic copolymer).

Preferably, the substantially nonaqueous carrier liquid has sufficientvolatility to evaporate essentially entirely from the coatingcomposition during the curing process, such as during heating at about176° C. to about 205° C. for about 8 to about 12 minutes. Suitablesubstantially nonaqueous carriers are known in the art, and include, forexample, aliphatic hydrocarbons like mineral spirits, kerosene, and highflash varnish makers and painters (VM&P) naphtha; aromatic hydrocarbons,like toluene, benzene, xylene and blends thereof (e.g. Aromatic Solvent100); alcohols, like isopropyl alcohol, n-butyl alcohol, and ethylalcohol; ketones, like cyclohexanone, ethyl aryl ketones, methyl arylketones, and methyl isoamyl ketone; esters, like alkyl acetates (e.g.ethyl acetate and butyl acetate); glycol ethers like ethylene glycolmonomethyl ether, ethylene glycol monoethyl ether, ethylene glycolmonobutyl ether (e.g. glycol ether EB), and propylene glycol monomethylether; glycol ether esters, like propylene glycol monomethyl etheracetate; aprotic solvents, like tetrahydrofuran; chlorinated solvents;mixtures of these solvents and the like.

The amount of substantially nonaqueous carrier included in thecomposition is limited only by the desired, or necessary, rheologicalproperties of the composition. Usually, a sufficient amount ofsubstantially nonaqueous carrier is included in the coating compositionto provide a composition that can be processed easily and that can beapplied to a metal substrate easily and uniformly, and that issufficiently removed from the coating composition during curing withinthe desired cure time.

Therefore, essentially any substantially nonaqueous carrier is useful inthe present coating composition as long as the substantially nonaqueouscarrier adequately disperses and/or solubilizes the compositioncomponents; is inert with respect to interacting with compositioncomponents; does not adversely affect the stability of the coatingcomposition or the ability of the corrosion-inhibition coating toinhibit corrosion of a metal substrate, and evaporates quickly,essentially entirely, and relatively rapidly to provide a cured coatingcomposition that inhibits the corrosion of a metal substrate,demonstrates good adhesion and flexibility, and has good chemical andphysical properties.

In preferred embodiments, the over-coat coating composition contains anover-coat cross-linker, preferably at from about 5 to about 30 percentby weight and more preferably at from about 6 to about 25 percent byweight of the under-coat composition on a non-volatile solids basis. Theover-coat cross-linker preferably contains at least two functionalgroups capable of undergoing chemical reaction with one or more of thepolyester (co)polymer, the under-coat cross-linker, the over-coatcross-linker, and/or the functional (meth)acrylic copolymer.

The choice of particular over-coat cross-linker typically depends on theparticular product being formulated. For example, some coatingcompositions are highly colored (e.g., gold-colored coatings). Thesecoatings may typically be formulated using cross-linkers that tend tohave a yellowish color. In contrast, white or clear coatings aregenerally formulated using non-yellowing cross-linkers, or only a smallamount of a yellowing cross-linker. Preferred cross-linkers aresubstantially free of mobile BPA, BPF, BADGE and BFDGE.

Any suitable hydroxyl-, amino-, vinyl- or isocyanate-functionalcross-linkers can be included in the over-coat coating composition. Forexample, phenoplast (i.e. phenolic), aminoplast, and blocked isocyanatecross-linkers may be used. The cross-linker may be in a variety offorms, including, for example, a monomer, a dimer, a trimer, anoligomer, a polymer or a (co)polymer. Preferably, the cross-linker is apolymeric material, more preferably a (co)polymer.

Examples of suitable cross-linkable aminoplast (co)polymers for use inthe over-coat coating composition include, without limitation:benzoguanamine-formaldehyde (co)polymers, melamine-formaldehyde(co)polymers, esterified melamine-formaldehyde (co)polymers, andurea-formadehyde (co)polymers. One specific example of a usefulaminoplast cross-linker is CYMEL 303 (Cytec Industries, Neuss, Germany).

Preferably, the over-coat cross-linker is a phenolic (i.e. phenoplast)(co)polymer. The preferred phenolic cross-linker contains at least twoterminal hydroxyl groups capable of undergoing chemical reaction with atleast one or more of the polyester (co)polymer, the over-coat phenolic(co)polymer, and/or the functional (meth)acrylic copolymer, therebyeffecting cross-linking within the under-coat and/or between theunder-coat and the over-coat.

Suitable phenolic cross-linkers for use in the over-coat coatingcomposition are commercially available. Examples of commerciallyavailable phenolic cross-linkers include those described above for theunder-coat coating composition.

The over-coat cross-linker may be selected to be a blocked isocyanatehaving two or more isocyanate functional groups, or an isocyanate groupand a vinyl group, capable of cross-linking with at least one componentof the coating composition. The blocked isocyanate may be an aliphaticand/or cycloaliphatic blocked polyisocyanate, for example HDI(hexamethylene diisocyanate), IPDI (isophorone diisocyanate), TMXDI(tetramethylene-m-xylidene diisocyanate), H₁₂NDI(bis[4-isocyanatocyclohexyl]methane), TMI(isopropenyldimethyl-benzylisocyanate), mixtures thereof, and dimers ortrimers thereof. Preferred blocking agents include, for example,n-butanone oxime, ε-caprolactam, diethyl malonate, and secondary amines.

Suitable commercially available blocked isocyanate cross-linkersinclude, for example, VESTANAT™ B 1358 A, VESTANAT™ EP B 1186 A,VESTANAT™ EP B 1299 SV (all available from Degussa Corp., Marl, Germany)and DESMODUR™ BL 3175 (available from Bayer A.G., Leverkusen, Germany).

The over-coat composition also preferably contains a functional(meth)acrylic (co)polymer (e.g., a carboxy-functional,hydroxy-functional, or oxirane-functional (meth)acrylic (co)polymer). Ina preferred embodiment, the functional (meth)acrylic (co)polymer isformed from at least one functional, ethylenically unsaturated monomeror oligomer (e.g., a carboxyl-functional, hydroxyl-functional oroxirane-functional vinyl monomer or oligomer) that is reacted with otherethylenically unsaturated (e.g. vinyl (meth)acrylic) co-monomers to formthe functional (meth)acrylic (co)polymer. The functional (meth)acrylic(co)polymer is preferably present in the over-coat composition in anamount from about 2.5 to about 30 percent by weight, more preferablyfrom about 5 to about 20 percent, and most preferably from about 7.5 to18 percent by weight of the over-coat composition on a non-volatilesolids basis.

The functional (meth)acrylic (co)polymer may have a weight averagemolecular weight (M_(w))from about 1,000 to about 50,000 Daltons (Da),more preferably from about 2,000 to about 25,000 Da, and most preferablyfrom about 5,000 to about 10,000 Da. The glass transition temperature ofthe functional (meth)acrylic (co)polymer preferably ranges from about−24° C. to about 105° C., and more preferably ranges from about 50° C.to about 90° C.

The functional (meth)acrylic (co)polymer preferably is capable ofundergoing cross-linking with one or more of the over-coat cross-linker,the under-coat cross-linker, and/or the polyester (co)polymer. Morepreferably, the functional (meth)acrylic (co)polymer is a (co)polymercontaining one or more functional groups selected from carboxyl,hydroxyl and oxirane. Most preferred functional (meth)acrylic(co)polymers contain at least one carboxyl group or one oxiranefunctional group, optionally in combination with one or more hydroxylgroups.

Preferably, the functional (meth)acrylic (co)polymer is a copolymer ofmethacrylic acid (MA) and acrylic acid (AA) with ethyl methacrylate andbutyl methacrylate; a copolymer of 2-hydroxyethylmethacrylate (HEMA)with ethyl methacrylate; a copolymer of glycidyl methacrylate (GMA) withethyl methacrylate, or a copolymer of glycidyl methacrylate withhydroxypropylmethacrylate and styrene. Preferably, the MA, AA or HEMAare present in the (co)polymer at from about 0.5 to about 10 percent,more preferably from about 1 to about 7.5 percent, and most preferablyfrom about 2 to about 5 percent by weight of the (co)polymer on a drysolids basis. Preferably, the GMA is present in the (co)polymer at fromabout 0.5 to about 40 percent, more preferably from about 10 to about 25percent, and most preferably from about 15 to about 20 percent by weightof the (co)polymer on a dry solids basis.

The functional (meth)acrylic (co)polymer preferably is chemicallysynthesized using suitable polymerization methods. Chemical synthesis ispreferred in order to control the chemical and physical properties(e.g., molecular weight, glass transition temperature, acid number, andthe like) of the functional (meth)acrylic (co)polymer. Preferredchemical synthesis methods involve polymerization of ethylenicallyunsaturated monomers (e.g. by free radical polymerization).

Suitable carboxyl-functional (meth)acrylic (co)polymers includepoly-acid or poly-anhydride polymers. Examples of such polymers include(co)polymers prepared from ethylenically unsaturated acid or anhydridemonomers (e.g., carboxylic acid or carboxylic anhydride monomers) andother ethylenically unsaturated co-monomers (e.g., vinyl-functionalco-monomers, particularly (meth)acrylic co-monomers).

A variety of carboxyl-functional and anhydride-functional monomers maybe used; their selection is dependent on the desired finalcarboxyl-functional (meth)acrylic (co)polymer properties. Suitableethylenically unsaturated carboxyl-functional monomers andanhydride-functional monomers for the present invention include monomershaving a reactive carbon-carbon double bond and an acidic or anhydridegroup. Preferred such monomers have from 3 to 20 carbons, 1 to 4 sitesof unsaturation, and from 1 to 5 acid or anhydride groups or saltsthereof. Methacrylic acid and acrylic acid are particularly preferredcarboxyl-functional monomers.

Suitable hydroxyl-functional (meth)acrylic (co)polymers include thoseobtained by polymerization of a hydroxyl-functional, ethylenicallyunsaturated monomer with other ethylenically unsaturated co-monomers(e.g., vinyl-functional co-monomers, particularly (meth)acrylicco-monomers). Preferred hydroxyl-functional monomers have from 3 to 20carbons, 1 to 4 sites of unsaturation, and from 1 to 5 hydroxyl groups.Specific examples of monomers containing a hydroxyl group are thehydroxy (C₁-C₆) alkyl (meth)acrylates such as, for example,2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropylmethacrylate, and 3-hydroxypropyl methacrylate.

Examples of suitable oxirane-functional (meth)acrylic (co)polymersinclude acrylate, methacrylate, and/or vinyl polymers and copolymershaving oxirane functional groups (including, e.g., (meth)acrylatecopolymers having pendant glycidyl groups). In one embodiment, theoxirane-functional (meth)acrylic (co)polymer is formed by reacting oneor more oxirane-functional monomers, optional hydroxy-functionalmonomers, and one or more other monomers (e.g., non-functionalmonomers). Preferred oxirane-functional (meth)acrylic (co)polymersutilized in this invention include those prepared by conventional freeradical polymerization of from about 0.5 to about 40, more preferablyfrom about 10 to about 25, and most preferably from about 15 to about 20percent by weight of the unsaturated oxirane-functional monomer with thebalance other ethylenically unsaturated co-monomers.

Specific examples of suitable oxirane-functional monomers containing aglycidyl group are glycidyl (meth)acrylate (i.e., glycidyl methacrylateand glycidyl acrylate), mono- and di-glycidyl itaconate, mono- anddi-glycidyl maleate, and mono- and di-glycidyl formate. It also isenvisioned that allyl glycidyl ether and vinyl glycidyl ether can beused as the oxirane-functional monomer. A preferred monomer is glycidylmethacrylate (“GMA”)

The choice of the ethylenically unsaturated co-monomer(s) is dictated bythe intended end use of the coating composition and is practicallyunlimited. Suitable ethylenically unsaturated hydroxyl-functionalmonomers for the present invention include monomers having a reactivecarbon-carbon double bond and a hydroxyl group. Examples of suitablealkyl (meth)acrylate esters include, but are not limited to, methyl,ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, isoamyl, hexyl,2-ethylhexyl, octyl, nonyl. decyl, isodecyl, lauryl, and isobornyl(meth)acrylates. Aromatic (meth)acrylate ester co-monomers (e.g.cyclohexyl and benzyl (meth)acrylate) may also be used. Preferred(meth)acrylic esters are the methyl and ethyl esters of methacrylic acidor mixtures of such esters.

Optional mono unsaturated monomers suitable for copolymerizing with theco-monomer containing a functional group include, but are not limitedto, vinyl monomers, like styrene, a halostyrene, isoprene,diallylphthalate, divinylbenzene, conjugated butadiene, α-methylstyrene,vinyl toluene, vinyl naphthalene, and mixtures thereof. Other suitablepolymerizable vinyl co-monomers include acrylonitrile, acrylamide,methacrylamide, methacrylonitrile, vinyl acetate, vinyl propionate,vinyl butyrate, vinyl stearate, isobutoxymethyl acrylamide, and thelike, and mixtures thereof.

A catalyst or polymerization initiator is ordinarily used in thepolymerization of the carboxyl-functional (meth)acrylic (co)polymers, insuitable amounts. For example, this can be virtually any free radicalinitiator that is sufficiently soluble in the co-monomer mixture andoptional carrier liquid to undergo decomposition to form radicals whenheated to a temperature at or above its decomposition temperature. Forexample, azoalkanes, peroxides, tertiary butyl perbenzoate, tertiarybutyl peroxypivalate, and tertiary butyl peroxyisobutyrate are suitable.Preferred initiators include azobis-isobutyronitrile (Trigonox B,Atofina Chemical Co.) and benzoyl peroxide.

The types of coating compositions that are found to be most effective inthe present invention are those that combine a polyester (co)polymerwith an under-coat cross-linker in an under-coat composition; and a PVC(co)polymer dispersion in a substantially nonaqueous over-coat carrierliquid with an over-coat cross-linker and a functional (meth)acrylic(co)polymer. An under-coat carrier liquid is thus not an essentialingredient of the under-coat composition. If an optional under-coatcarrier liquid is used, it is typically a substantially nonaqueousorganic solvent or solvent blend to affect more rapid removal of thecarrier liquid and more rapid curing of the under-coat composition uponapplication to the substrate.

A substantially nonaqueous organic solvent can include a relatively lowamount of water, such as up to about five percent by total weight of theover-coat coating composition, without adversely affecting the metalcorrosion-inhibiting properties of the over-coat coating composition,either prior to or after curing. The water can be added to thecomposition intentionally, or can be present in the compositioninadvertently, such as when water is present in a particular componentincluded in the coating composition.

Substantially nonaqueous organic solvents or organic solvent blends maybe used advantageously as the under-coat carrier liquid, for example, toobtain more favorable coating rheology, to achieve faster drying or curetimes, or to effectively dissolve or solvate another component of theunder-coat composition (e.g. the polyester (co)polymer or the under-coatcross-linker). Preferably, the substantially nonaqueous carrier liquidis selected to have sufficient volatility to evaporate essentiallyentirely from the coating composition during the curing process, such asduring heating at about 175-205° C. for about 8 to about 12 minutes.

Organic solvents that are particularly useful as optional under-coatcarrier liquids include aliphatic hydrocarbons (e g , mineral spirits,kerosene, high flashpoint VM&P naptha, and the like); aromatichydrocarbons (e.g., benzene, toluene, xylene, solvent naphtha 100, 150,200 and the like); alcohols (e.g. ethanol. n-propanol, isopropanol,N-butanol, iso-butanol and the like); ketones (e.g. 2-butanone,cyclohexanone, methyl aryl ketones, ethyl aryl ketones, methyl isoamylketones, and the like); esters (e.g. ethyl acetate, butyl acetate andthe like); glycols (e.g. butyl glycol), glycol ethers (e.g.methoxypropanol); glycol ethers (e.g. ethylene glycol monomethyl ether,ethylene glycol monoethyl ether, ethylene glycol monobutyl ether,propylene glycol monomethyl ether, and the like); glycol esters (e.g.butyl glycol acetate, methoxypropyl acetate and the like); and mixturesthereof.

The amount of nonaqueous carrier included in the under-coat compositionis limited primarily by the desired, or necessary, rheologicalproperties for application of the composition to the substrate.Preferably, a sufficient amount of nonaqueous carrier is included in theunder-coat coating composition to provide a composition that can beprocessed easily and that can be applied to a metal substrate easily anduniformly, and that is sufficiently removed from the coating compositionduring curing within the desired cure time.

Therefore, essentially any substantially nonaqueous carrier is useful inthe present under-coat coating composition as long as the substantiallynonaqueous carrier adequately disperses and/or solubilizes theunder-coat composition components; is inert with respect to interactingwith composition components; does not adversely affect the stability ofthe coating composition or the ability of the corrosion-inhibitioncoating to inhibit corrosion of a metal substrate; evaporates quickly,essentially entirely, and relatively rapidly to provide a cured coatingcomposition that inhibits the corrosion of a metal substrate,demonstrates good adhesion and flexibility, and has good chemical andphysical properties.

One optional ingredient is a catalyst to increase the rate of cure orcross-linking in one or both of the under-coat and second coatcompositions. Generally, acid catalysts can be used to accelerate therate of cure of either or both of the under-coat and over-coat coatingcompositions. In some embodiments, the catalyst is present in an amountof 0.05 to about 5 percent, and preferably about 0.1 to about 1.5percent, by weight of nonvolatile material.

Examples of suitable catalysts, include, but are not limited to,quaternary ammonium compounds, phosphorous compounds, and tin and zinccompounds, like a tetraalkyl ammonium halide, a tetraalkyl or tetraarylphosphonium iodide or acetate, tin octoate, zinc octoate,triphenylphosphine, combinations thereof, and similar catalysts known topersons skilled in the art.

Catalysts that are particularly suitable for accelerating the rate ofcure for the under-coat composition include, for example, phosphoricacid solutions (e.g. an 85% aqueous phosphoric acid solution in butylglycol at a 1:1 weight ratio), phosphoric acid ester solutions (e.g.ADDITOL XK 406™, available from Cytec Surface Specialties, Inc., WestPaterson, N.J.), and dodecylbenzene sulfonic acid (e.g. CYCAT 600™available from Cytec Surface Specialties, Inc., West Paterson, N.J.).Additionally or alternatively, tin catalysts can be used, preferably amixture of mono- and di-octyl tin-mercaptides (e.g. TINSTAB OTS 17 MS™available from AKZO-Nobel Chemicals, Inc., Chicago, Ill.), or dibutyltindilaurate (e.g. FASCAT™ available from Atofina Chemicals, Inc.,Philadelphia, Pa.).

Catalysts that are particularly suitable for accelerating the rate ofcure for the over-coat composition include, for example, aluminumcatalysts (e.g. aluminum sec-butoxide, AKZO-Nobel Chemicals, Inc.,Chicago, Ill.).

Coating compositions that are to be used as an internal can protectivecoating typically include a natural or synthetic lubricant. Suitablelubricants include, for example, long-chain aliphatic waxes, carnubawaxes (e.g. Luba-Print 887/C Wax Dispersion available from L. P. Bader &Co., GmbH, Rottweil, Germany) synthetic wax dispersions (e.g. LancoGlidd 4518V available from Lubrizol, Corp., Wickliffe, Ohio),poly(tetrafluoroethylene) waxes, and mixtures, blends or dispersionsthereof.

Because of the use of a PVC (co)polymer organosol in the inventivemulti-coat coating system, the protective coating may be susceptible tothe coating darkening effects of dehydrochlorination and autocatalyticoxidative cross-linking of PVC (co)polymer. Accordingly, in onepreferred embodiment of this invention, a PVC stabilizer (i.e. ahydrogen chloride scavenger) has been used advantageously as an additiveto the over-coat coating composition. Alternatively, the PVC stabilizermay be added to the under-coat composition or to both the under-coat andover-coat composition. The PVC stabilizer is preferably present in anamount from about 0.1 up to about 30 percent by weight of the coatingcomposition on a non-volatile solids basis.

Examples of suitable PVC stabilizers include organotin esters such asdibutyl tin dilaurate; maleates, especially dibutyl tin maleate; andmono- and di-octyl tin mercaptides (e.g. TINSTAB OTS 17 MS™, AKZO-NobelChemicals, Inc., Chicago, Ill.), which are particularly preferred.Suitable PVC stabilizers also include oxirane-functional chemicalcompounds that are at least substantially free of BPA, BPF, BADGE andBFDGE. The oxirane-functional chemical compound is preferably selectedfrom epoxidized linseed oil, epoxidized soy bean oil, dimer acid ofdiglycidyl ether (DGE) and epoxidized polybutadiene. A GMA-functional(meth)acrylic (co)polymer (i.e., the functional (meth)acrylic(co)polymer of the over-coat composition) may also function as a PVCstabilizer.

In some embodiments, a pigment can be added to the under-coat, theover-coat, or both the under-coat and the over-coat compositions.Suitable pigments, such as aluminum flake, titanium dioxide and zincoxide, may be added to improve the appearance of the protective coating,or to act as scavengers for hydrogen sulfide emitted by foodstuffs thatacts to stain or darken the protective coating. A pigment like aluminumflake can be present in one or both of the under-coat coatingcomposition and over-coat coating composition, typically at aconcentration from about 2 to about 15 percent by weight, and moretypically from about 5 to about 10 percent by weight of the compositionon a non-volatile solids basis. A pigment like titanium dioxide can alsobe present in one or both of the under-coat coating composition andover-coat coating composition, preferably in an amount from about 35 toabout 50 percent by weight, and more preferably from about 40 to about45 percent by weight of the coating composition. Zinc oxide can also bepresent in one or both of the under-coat coating composition andover-coat coating composition, preferably in an amount from about 0.5 toabout 30 percent by weight, and more preferably from about 5 to about 15percent by weight of the coating composition.

In some embodiments, one or more additional (co)polymer components maybe added to one or both of the under-coat and over-coat compositions.Examples of suitable (co)polymers include solution vinyl (PVC)(co)polymers, solution poly(vinyl)butyral (co)polymers, dispersed orsolution meth(acrylic) copolymers, solution polyester (co)polymers, andmixtures thereof. Suitable polymers are commercially available, andinclude UCAR™ solution vinyl (co)polymers (available from Dow ChemicalCo., Midland Mich.), BUTVAR™ solution poly(vinyl)butyral (co)polymers(available from Solutia, Inc., Philadelphia, Pa.), ELVACITE solution(meth)acrylic (co)polymers, and VITEL™ solution polyester (co)polymers.

In one preferred embodiment, UCAR VMCA™ solution vinyl (co)polymer (DowChemical Co., Midland Mich.) is added to the over-coat composition in anamount from about one to about ten percent by weight of the over-coatcoating composition, and more preferably from about two to about fivepercent by weight of the over-coat coating composition.

Depending upon the desired application, the under-coat or over-coatcoating compositions may include other additives such as water,coalescing solvents, leveling agents, surfactants, wetting agents,dispersants (e.g. lecithin), defoamers (e.g. modified (poly)siloxanes),thickening agents (e.g. methyl cellulose), cure accelerators, suspendingagents, adhesion promoters, cross-linking agents, corrosion inhibitors,fillers (e.g. titanium dioxide, zinc oxide, aluminum), matting agents(e.g. precipitated silica) and the like, and combinations thereof.

The coating compositions of the present invention may be prepared byconventional methods, but preferably comprise an under-coat compositionand an over-coat composition. The under-coat composition is preferablycoated on a surface of a metal substrate, and the over-coat compositionis preferably coated on the at least partially cured (hardened)under-coat composition.

The under-coat coating compositions of the present invention may beprepared in various ways. For example, the under-coat coatingcomposition may be prepared by simply admixing the polyester(co)polymer, the under-coat phenolic cross-linker, and any optionalingredients, in any desired order, with sufficient agitation. Theresulting mixture may be admixed until all the composition ingredientsare substantially homogeneously blended.

Alternatively, the under-coat coating composition may be prepared as aliquid solution or dispersion by admixing to an optional under-coatcarrier liquid the polyester (co)polymer, the under-coat phenoliccross-linker, and any optional ingredients, in any desired order, withsufficient agitation. An additional amount of the under-coat carrierliquid may be added to the under-coat coating composition to adjust theamount of nonvolatile material in the coating composition to a desirablelevel for effective coating. For example, the under-coat coatingcomposition may be prepared by adding the phenolic (co)polymer materialto a solution of the polyester (co)polymer in a solvent mixture that mayinclude an alcohol and/or a small amount of water.

Where, as preferred, the under-coat coating composition is applied as aliquid coating, the under-coat coating composition is typically producedby intensive mixing of the raw materials at temperatures of from about10° C. to about 50° C., and more preferably from about 15° C. to about35° C., to obtain a substantially homogenous liquid solution. Whenapplied as a liquid coating, the under-coat coating compositiontypically exhibits a solids content from about 25 to about 70 percent byweight nonvolatile material, and more preferably from about 30 to about50 percent by weight nonvolatile material.

The over-coat coating composition is preferably applied as a dispersionof solids in an over-coat carrier liquid, and preferably exhibits asolids content from about 25 to about 70 percent, and more preferablyfrom about 35 to about 65 percent by weight nonvolatile material. Theover-coat coating composition is typically produced by intensivehigh-shear mixing or media-milling of the raw materials at temperaturesof preferably from about 10° C. to about 48° C., and more preferablyfrom about 15° C. to about 35° C., to obtain a substantially homogenousliquid dispersion.

If either the under-coat or over-coat coating compositions are preparedwith optional components, such as a pigment, the steps of preparationmay be varied accordingly. In embodiments of the present invention thatincorporate pigments, such as aluminum flake, zinc oxide and titaniumdioxide, the resulting pigmented coating composition typically has apigment-to-binder ratio of about 0.5:1 to about 0.85:1, and moretypically about 0.6:1 to about 0.7:1. Pigment-to-binder ratio is ameasure, on the basis of weight, of parts of pigment for every 1 part of(co)polymer, or non-pigment, which includes all coating components thatare not pigment and not volatilized after the curing step.

The hardenable coating compositions of the present invention are useful,for example, as protective coatings to prevent contamination offoodstuffs contained in a metal packaging container by the packagingmetal or the protective lacquer and to prevent attack by the foodstuffson the metal container. The inventive protective coating compositionsare particularly effective at imparting resistance to attack by acidicfoodstuffs and beverages. The compositions are especially useful incoating food or beverage cans, particularly the interiors of such cans,where their virtually undetectable levels of BPA and aromatic glycidylether chemical compounds and their other chemical, physical andmechanical properties make them particularly desirable.

The aforementioned coating compositions are particularly well adaptedfor use as an internal surface coating for multi-part foodstuffspackaging containers (e.g., two-piece cans, three-piece cans, etc.).Two-piece cans are manufactured by joining a can body (typically a drawnmetal body) with a can end closure (typically a drawn metal end). Theinventive coating compositions are well suited for use in food contactsituations and may be used on the inside of such cans and componentsused in fabricating foodstuffs containers. The multi-coat coatingsystems of the present invention are particularly well suited forproviding a protective coating to the interior surface of “easy-open”end closures used in fabricating containers for foodstuffs andbeverages, particularly for vacuum-packed foodstuffs.

Protective coatings for fabricating food and beverage containers may beapplied to metal substrates and cured into films at high speed, onhigh-speed coating lines (e.g., coil coating lines). The coating agentsare typically applied in a roller coating process either continuously oncoil lines or batch-wise on sheet coating lines to thin metals such asaluminum, tinplate, tin free steel or chromed steel, and then reacted athigh temperatures. The coated metals thus produced are then shaped toform the desired metal packaging articles by processes such as, forexample, deep-drawing, stamping, creasing and flanging. This machiningrequires very high flexibility and excellent adhesion of the coatingagents used. In such applications, the coatings preferably should notexperience any change in the protective function due to the reshapingprocesses and, in addition, should preferably exhibit suitable adhesionand have intact surfaces.

Modern high-speed coil coating lines typically require coatings thatwill dry and cure within a few seconds when heated rapidly to peak metaltemperatures of 420° F. to 550° F. (about 215° C. to about 300° C.).Many metal packaging articles, after filling with the foods, aresubjected to exposure to similar high temperature in thermal processesfor food preservation (e.g. pasteurization or sterilization). Afterthese high temperature thermal processes, the protective coatingsideally exhibit little or no change with respect to protective function,adhesion, flexibility, appearance, or chemical composition.

The inventive multi-coat systems can be applied as coatings to a varietyof metal substrates such as tinplate, tin free steel, aluminum and itsalloys, and the like. The compositions can be applied as a film byconventional means such as, for example, brushing, roller coating orspraying. Roller coating is the preferred method when coating flat metalfor can manufacture and spraying is preferred when coating preformedcans.

Preferably, the under-coat composition is applied as a substantiallyuniform and continuous defect-free layer or film on the metallicsubstrate used, and the over-coat composition is applied on the curedunder-coat composition as a substantially uniform and continuousdefect-free layer or film. Preferably, the under-coat and over-coatlayers are substantially free from surface defects, such as, forexample, craters, pinholes, and de-wet regions.

Metal coatings are generally applied to metal sheets in one of two ways,each of which involves different coating and curing conditions. Thecoated metal sheets may be fabricated into can bodies or ends in a laterstage of the manufacturing operation.

One process, called the sheet bake process, involves roll coating largemetal sheets. These sheets are then placed upright in racks and theracks are typically placed in ovens for about 10 minutes to achieve peakmetal temperatures of about 180° C. to about 205° C. In a second processknown as coil coating, large rolls of thin gage metal (e.g., steel oraluminum) are unwound, roll coated, heat cured and rewound. During thecoil coating process, the total residence time in the curing ovens willvary from about 2 seconds to about 20 seconds with peak metaltemperatures typically reaching about 215° C. to about 300° C.

The present invention may be useful as a spray applied, liquid coatingfor the interior of two-piece drawn and ironed tinplate food cans(hereinafter “tinplate D&I cans”). The present invention also offersutility in other metal substrate coating applications. These additionalapplications include, but are not limited to: coil coating, sheetcoating, and the like.

A coil coating is described as the coating of a continuous coil composedof a metal (e.g., steel or aluminum). Once coated, the coating coil istypically subjected to a short thermal, ultraviolet, and/orelectromagnetic curing cycle, which lead to the drying and curing of thecoating. Coil coatings provide coated metal (e.g., steel and/oraluminum) substrates that can be fabricated into formed articles such astwo-piece food cans, three-piece food cans, food can ends, beverage canends and the like.

A sheet coating is described as the coating of separate pieces of avariety of materials (e.g., steel or aluminum) that have been pre-cutinto square or rectangular ‘sheets’. Typical dimensions of these sheetsare approximately one square meter. Once coated, each sheet is cured.Once dried and cured, the sheets of the coated substrate are collectedand prepared for subsequent fabrication. Sheet coatings provide coatedmetal (e.g., steel or aluminum) substrate that can be successfullyfabricated into formed articles such as two-piece food cans, three-piecefood cans, food can ends, drawn and ironed cans, beverage can ends andthe like.

In a preferred embodiment, the method of the present invention includesapplying an under-coat coating composition of the present invention ontoa surface of a metal substrate to form a first coating layer, heatingthe coated substrate so that the first coating layer at least partiallycures to form a cured film adhered to the substrate surface, applying anover-coat coating composition of the present invention onto the firstcoating layer to form a second coating layer, and heating the coatedsubstrate so that the second coating layer at least partially cures toform a cured film adhered to the first coating layer. The first coatinglayer and the second coating layer may be applied in a single pass, inmultiple passes, or in combination with additional coating layers placedbetween the metal substrate and the first coating layer (e.g. a primingor subbing layer) or on top of the second coating layer. In someembodiments, one or more intermediate layers may be included between thefirst and second coating layers.

The preferred method of applying coating compositions of the presentinvention to metal substrates is roll coating (e.g., by direct rollcoating, reverse roll coating, rotogravure coating, and the like). Thecoating compositions can generally be roll coated to produce cured filmshaving overall multi-coat film weights of about 8 g/m² to about 28 g/m².

In some embodiments, the under-coat and over-coat compositions, afterapplication to the metal substrate, are at least partially cured (i.e.hardened or cross-linked) by exposure to heat, actinic radiation (e.g.ultraviolet or infrared curing), electromagnetic radiation (e.g.electron beam curing), combinations thereof and the like. In certainpreferred embodiments, the under-coat composition on the metal substrateis at least partially cross-linked before applying the over-coatcomposition.

The applied under-coat and over-coat coating compositions can be driedand cured by heating to drive off at least a portion of any carrierliquids and/or to accelerate a cross-linking reaction. The coatedcomposition is typically heated to 150-220° C. for 1 to 20 minutes inorder to form a dried, cured film.

If the coating is applied using a sheet-bake process, the coated metalsubstrate is preferably cured at a temperature of about 175° C. to about205° C. for about 8 to about 10 minutes. In contrast, when the coatingis carried out using a coil-coating process, the coated metal substrateis preferably cured by heating for about 2 to about 20 seconds at atemperature of about 230° C. to about 300° C.

The hardened protective coating compositions of the present inventionpreferably exhibit good adhesion to both the metal substrate and withinthe coated layers (i.e. inter-coat adhesion). The hardened coatingcompositions on metal substrates may be shaped mechanically to formfoodstuffs containers or “easy-open” end closures; for example bydeep-drawing, creasing and flanging. After forming, the metal containersmay be filled with a foodstuff, and then sterilized. The hardenedprotective coating compositions of the present invention exhibit goodflexibility and chemical resistance, especially in the presence offoodstuffs containing acetic acid, citric acid and/or lactic acid,without exhibiting loss of adhesion or discoloration.

The examples that follow are intended to illustrate the preparation anduse of the presently described invention, but are not intended to belimiting in any way.

EXAMPLES

Examples 1-6 illustrate the chemical synthesis of exemplary polyester(co)polymers according to the present invention. Examples 7-12illustrate the chemical synthesis of exemplary functional (meth)acrylic(co)polymers containing carboxyl, hydroxyl or oxirane functionality.Examples 13-15 illustrate the preparation of exemplary under-coatcoating compositions containing a polyester (co)polymer and anunder-coat cross-linker. Examples 16-18 illustrate the preparation ofexemplary over-coat coating compositions containing a PVC (co)polymerdispersed in a substantially nonaqueous carrier liquid, an over-coatcross-linker, and a functional (meth)acrylic (co)polymer. Examples 19-22illustrate use of the exemplary under-coats and over-coats of thepresent invention to provide protective coatings to metal substrates.Examples 23-25 are comparative examples.

Examples 1-6 Synthesis of Polyester (Co)polymers

The following general method was used to produce polyesters partlyobtained by trans-esterification of esters of dicarboxylic acids (e.g.dimethylterephtalate), as in Example 1. The raw materials of Table I,Example 1 (all available from Sigma-Aldrich Chemical Company, St. Louis,Mo.), except the terephthalic acid, were charged to the reaction vesselof a reaction apparatus (equipped with an overhead fractionating columnand Dean-Stark condenser for removing water, an overhead stirrer, and anitrogen inlet) in the order listed in Table I. The charged reactantswere heated while stirring under a dry nitrogen (N₂) blanket until theonset of methanol distillation. Heating was continued to maintain theoverhead column temperature at about 73-75° C. with removal of methanoluntil 90% of the theoretical amount of methanol was removed.

Then the terephthalic acid was added and heating continued with removalof water while maintaining the temperature at the column head between99-102° C. The temperature of the product was allowed to increaseprogressively to about 230° C. The acid and hydroxyl values were checkedregularly, and the reaction was stopped by cooling when the hydroxylvalue of the polyester reached a value of about 30-40 mg KOH/gpolyester, and the acid number reached a value of about 5 mg KOH/gpolyester.

The following general method was used to produce a series of exemplarypolyester (co)polymers based on diacids, as in Examples 2-6. The rawmaterials of Table I, Examples 2-6, all available from Sigma-AldrichChemical Company (St. Louis, Mo.), were charged to the reaction vesselof the reaction apparatus of Example 1 in the order listed in Table I.The charged reactants were heated while stirring under a dry nitrogen(N₂) blanket until the onset of water distillation. Heating wascontinued with removal of water while maintaining the temperature at thehead of the column between 99-102° C. The temperature of the product wasallowed to increase progressively to about 230° C. The acid and hydroxylnumbers were checked regularly and the reaction was stopped by coolingwhen the hydroxyl number of the polyester reached a value of about 25-35mg KOH/g polyester and the acid number reached a value of about 5 mgKOH/g polyester.

TABLE I Preparation of Polyester (Co)polymers (Examples 1-6) Example 1Example 2 Example 3 Example 4 Example 5 Example 6 Raw Material (% w/w)(% w/w) (% w/w) (% w/w) (% w/w) (% w/w) Ethylene Glycol 6.00 0.00 1.000.00 0.00 1.06 Propylene Glycol 19.40 0.00 3.30 0.00 0.00 3.37Diethylene Glycol 0.00 22.50 19.00 26.48 36.42 18.88 Neopentyl Glycol0.00 15.00 13.00 0.00 0.00 13.39 Trimethylolpropane 4.20 2.00 2.30 1.961.96 2.41 Dimethylterephthalate 58.0 0.00 0.00 0.00 0.00 0.00Isophthalic Acid 0.00 30.50 25.40 29.24 28.54 25.34 Terephthalic Acid12.40 30.00 36.00 28.73 28.03 35.55 Cyclohexane 0.00 0.00 0.00 13.600.00 0.00 Dimethanol Dimer fatty acid 0.00 0.00 0.00 0.00 5.05 0.00Product — — — — — — Characteristics Percent Nonvolatile 52.0 53.0 52.552.5 53.4 52.0 Solids (% w/w) Hydroxyl Number 39 25 34 27 24 30 (mgKOH/g solids) Viscosity (mPa-sec) 5 4 4.5 4.9 3.7 —

Examples 7-9 Synthesis of Carboxyl-Functional (Meth)acrylic (Co)polymer

The following general method was used to produce the three exemplarycarboxyl-functional (meth)acrylic (co)polymers of Examples 7-9 as shownin Table II. The raw materials from Table II are available from thesuppliers listed in Table II. The percentages given in the table arestandardized to 100 percent on a weight basis.

TABLE II Preparation of Carboxyl-functional (Meth)acrylic Copolymers RawMaterial Example 7 Example 8 Example 9 Available From (% w/w) (% w/w) (%w/w) Raw Material Solvesso Exxon/Mobil 37.56 30.35 37.46 100 ™ Over-coatChemical Co., Carrier Liquid Houston, TX Butyl Elf Atochem, Inc., 0.0046.51 0.00 Methacrylate Philadelphia, PA Ethyl Elf Atochem, Inc., 46.220 46.1 Methacrylate Philadelphia, PA Methacrylic Elf Atochem, Inc., 2.291.85 0.00 Acid Philadelphia, PA Acrylic Acid Elf Atochem, Inc., 0.000.00 1.92 Philadelphia, PA Trigonox B ™ AKZO-Nobel 1.21 1.63 2.00di-tert butyl Chemicals, Inc., peroxide Chicago, IL Initiator ButylGlycol BP/Shell 12.72 19.66 12.52 Over-coat Chemicals, Carrier LiquidHouston, TX Product — — — — Characteristics Percent Non- — 50.1 48.950.5 volatile Solids (% w/w) Acid Number — 29.8 25.5 28.5 (mg KOH/gsolids)

The Solvesso 100™ carrier liquid was added to a glass reaction flaskequipped with a mechanical stirrer, a condenser, a nitrogen inlet, athermocouple connected to a temperature controller, and a heating mantleconnected to the temperature controller. The reaction flask wasblanketed with dry nitrogen (N₂) and heated to about 125-130° C. Themonomers from Table II were then added to the heated reaction flask inthe order listed, and the Trigonox B™ di-tert butyl peroxide initiatorwas added to initiate the free radical polymerization.

After the initiator addition, the reaction mixture was maintained at125° C.-130° C. for about four hours. Then the butyl glycol was added toreduce the non-volatile solids content of the copolymer solution. Thefinal carboxyl-functional (meth)acrylic (co)polymer products exhibitedan acid number of about 25-30 mg KOH/g (co)polymer. Thecarboxyl-functional (meth)acrylate (co)polymers contained about 1.85-2.3percent of methacrylic acid or acrylic acid by weight on a dry solidsbasis.

Example 10 Synthesis of Hydroxyl-Functional (Meth)acrylic (Co)polymer

The following example illustrates the preparation of ahydroxyl-functional (meth)acrylic (co)polymer as shown in Example 10.The compositional ingredients of the (co)polymer of Example 10 areincluded below in Table III.

TABLE III Preparation of Hydroxyl-functional (Meth)acrylic Copolymer RawMaterial Available Example From 10 (g) Raw Material Diisobutyl ketoneBP/Shell Chemicals, Inc., 23,780.0 Houston, TX Trigonox B ™ AKZO-NobelChemicals, 54.5 di-tert butyl peroxide Inc., Initiator Chicago, ILVAZO-64 Wako Chemicals U.S.A., 54.5 azobis isobutyronitrile Dallas, TXInitiator Ethyl Methacrylate Elf Atochem, Inc., 19,120.0 Philadelphia,PA 2-Hydroxyethylmethacrylate Elf Atochem, Inc., 1,000.0 Philadelphia,PA Trigonox B ™ AKZO-Nobel Chemicals, 236.1 di-tert butyl peroxide Inc.,Initiator Chicago, IL VAZO-64 Wako Chemicals U.S.A., 204.3 azobisisobutyronitrile Dallas, TX Initiator n-dodecyl mercaptan Sigma-AldrichChemical Co., 118.0 Chain Transfer Agent St. Louis, Missouri ProductCharacteristics — — Percent Non-volatile — 46 Solids (% w/w) HydroxylNumber — 30-35 (mg KOH/g solids)

Diisobutyl ketone (23.78 kg) was added to a clean dry reaction vesseland blanketed with dry nitrogen (N₂). The diisobutyl ketone was heatedto 110° C. Then 54.5 g Trigonox B™, a di-t-butylperoxide polymerizationinitiator available from AKZO-Nobel Chemicals, Inc. (Chicago, Ill.), and54.5 g VAZO 64, an azobis isobutyronitrile polymerization initiatoravailable from Wako Chemicals U.S.A. (Dallas, Tex.), were added to theheated diisobutyl ketone.

In a separate vessel a monomer premix containing 19.12 kg of ethylmethacrylate, 1 kg of 2-hydroxyethylmethacrylate, 204.3 g VAZO 64, 118.0g of n-dodecyl mercaptan, and 236.1 g of Trigonox B™ was prepared. Afterfive minutes, ten weight percent of the monomer premix was quickly addedto the reaction vessel. The remaining 90 weight percent of the monomerpremix was then added slowly to the reaction vessel over a three hourtime period while maintaining the temperature of the reaction mixture atabout 110° C. After the three-hour monomer addition period, the vesselholding the monomer mix was then rinsed with 331.4 g of diisobutylketone, which was added to the reactor. After the entire monomer blendand rinse was added to the reactor, the reaction mixture was held at110° C. for an additional 30 minutes. Then, while maintaining thereaction temperature at 110° C., a solution of 308.7 g of t-butylperoctoate in 308.7 g of diisobutyl ketone was added to the reactionmixture in twelve equal portions at 15-minute intervals. The resultingreaction mixture was held at 110° C. for 60 minutes, then cooled. Theresulting reaction product contained 46% by weight of the ethylmethacrylate-2-hydroxyethyl methacrylate copolymer. Thehydroxyl-functional (meth)acrylate (co)polymer contained about 95% ethylmethacrylate and 5% 2-hydroxyethyl methacrylate by weight on a drysolids basis.

Examples 11-12 Synthesis of Oxirane-Functional (Meth)acrylic(Co)polymers

The following examples (the compositional ingredients of which aresummarized below in Table IV) illustrate the preparation ofoxirane-functional (meth)acrylic (co)polymers useful in the presentinvention. Additional examples are provides by Example 1, Runs 1-4, ofco-pending published U.S. Patent Application 20040259989, titled“Aqueous Dispersions and Coatings,” filed Apr. 2, 2004, which isincorporated herein by reference. Other suitable examples are providedin issued U.S. Pat. No. 6,916,874, filed Aug. 2, 2002 and assigned to acommon assignee, which is incorporated herein by reference.

TABLE IV Preparation of Oxirane-functional (Meth)acrylic Copolymers RawMaterial Example Example Raw Material Available From 11 (g) 12 (g)n-Butanol Exxon/Mobil 245.0 0.0 Over-coat Carrier Liquid ChemicalHouston, TX Butyl Cellosolve ™ BP/Shell Chemicals, 804.0 0.0 Over-coatCarrier Liquid Houston, TX Di-isobutyl ketone Dow Chemical Co., 0.0132.3 Over-coat Carrier Liquid Midland, MI t-butyl peroctoate, InitiatorSigma-Aldrich 14.2 0.0 St. Louis, MO Styrene Sigma-Aldrich 1162.0 0.0St. Louis, MO 2-Hydroxyethylmetha- Elf Atochem, Inc., 888.0 0.0 crylatePhiladelphia, PA Glycidyl methacrylate Sigma-Aldrich 64.1 105.8 Ethylmethacrylate Atofina Chemicals — 423.6 Philadelphia, PA t-butylperoctoate, Initiator Atofina Chemicals 90.4 0.0 Philadelphia, PAt-butyl peroxide, Initiator Aztec Peroxides, 21.2 Houston, TX ButylCellosolve ™ Aztec Peroxides, 105.0 201.2 Over-coat Carrier LiquidHouston, TX t-butyl peroctoate Aztec Peroxides, 14.2 0.0 Houston, TXLuperox DTA ™ Atofina Chemicals 0.0 21.2 Philadelphia, PA ButylCellosolve ™ Atofina Chemicals 27.0 94.7 Over-coat Carrier LiquidPhiladelphia, PA t-butyl peroctoate Atofina Chemicals 3 × 4.34 0.0Philadelphia, PA Percent Non-volatile — — 55.0 Solids (% w/w)

In Example 11, a reaction apparatus equipped with a reaction flask,stirrer, reflux condenser, thermocouple, heating mantle and nitrogenblanket was provided. To the flask was added 245 g n-butanol and 804 gbutyl Cellosolve™. The reaction flask was then blanketed with drynitrogen (N₂). The flask was heated to 98° C., and 14.2 g t-butylperoctoate were added. In a separate vessel, a monomer premix wasprepared containing 1162 g styrene, 888 g 2-hydroxy ethyl methacrylate,64.1 g glycidyl methacrylate, and 90.4 g t-butyl peroctoate.

After five minutes the monomer premix was added to the flask over twoand a half hours while maintaining the temperature at 97° C. to 101° C.An initiator premix comprising 105 g butyl Cellosolve™ and 45.1 gt-butyl peroctoate was then prepared. When the monomer premix additionwas complete, the premix vessel was rinsed with 43 g butyl Cellosolve.The initiator premix was then added over a one hour period. When theinitiator premix addition was complete, the vessel was rinsed with 27 gbutyl Cellosolve™.

The batch was held at 98° C. to 99° C. for one hour. At the end of thehour 4.34 g t-butyl peroctoate were added and the batch was held for onehour. At the end of the hour a second addition of 4.34 g t-butylperoctoate was made and the batch was held an additional one hour. Atthe end of the hour a third addition of 4.34 g t-butyl peroctoate wasmade and the batch was held one hour. The batch was then cooled,yielding an oxirane-functional (meth)acrylic (co)polymer having anoxirane value of 0.018 equivalents/100 grams solid (co)polymer, an acidnumber of approximately 2-3 mg KOH/g (co)polymer, and a non-volatilesolids content of 62.5 percent by weight.

Example 12, a reaction apparatus equipped with a reaction flask,stirrer, reflux condenser, thermocouple, heating mantle and nitrogenblanket was provided. The reaction flask was then blanketed with drynitrogen (N₂). To the flask was added 132.3 g of Di-isobutyl ketone(DIBK). The flask was heated to 140° C. In a separate vessel, a monomerpremix was prepared containing 423.6 g of ethyl methacrylate, 105.8 g ofglycidyl methacrylate and 21.2 g of the catalyst di-t-Butyl Peroxide.These ingredients were mixed for about 30 minutes, then added to thereaction flask over a four hour period. The temperature was maintainedat about 140-145° C. The reflux rate was low to moderate.

After the four-hour addition period, the batch was held for 90 minutesat 140-145° C. About one hour before the end of the hold, a premixcontaining 201.2 g of butyl cellosolve™ and 21.2 g of Luperox DTA™ wasprepared and allowed to mix for about 30 minutes. About 30 minutesbefore the end of the 90-minute hold, the temperature was slowlyincreased to about 145-150° C. At the end of the 90-minute hold, thebutyl Cellosolve™/Luperox DTA™ were added to the reaction flask overabout two hours while maintaining a temperature of about 145-150° C.After another two-hour hold, 94.8 g of butyl Cellosolve™ was added andthe batch was allowed to cool to 120° C., with continued cooling to 60°C. and then room temperature.

Example 13-15 Preparation of Exemplary Under-Coat Coating Compositions

In Example 13, an exemplary (a) under-coat coating compositionscontaining (i) a polyester (co)polymer, and (ii) an (blocked isocyanate)under-coat cross-linker, were prepared using the materials and accordingto the formulation summarized in Table V below.

TABLE V Preparation of Exemplary Under-coat Coating Composition RawMaterial Example Raw Material Available From 13 (g) Dibutyl Ether (DBE)DuPont Chemical Corp., 80.0 Under-coat Carrier Liquid Wilmington, DEAromatic 100 Solvent Exxon-Mobil Chemical Co. 80.0 Under-coat CarrierLiquid Houston, TX Eastman EB ™ Solvent Eastman Chemical Co. 40.0Under-coat Carrier Liquid Knoxville, TN Vestanat B 1358A ™ Degussa, A.G.22.1 2-butanone oxime Marl, Germany blocked-isocyanate Under-coatCross-linker Dynapol L 952 ™ Degussa, A.G. 133.4 Polyester (co)polymerMarl, Germany Aromatic 100 Solvent Exxon-Mobil Chemical Co. 25.1Under-coat Carrier Liquid Houston, TX A-2291FG Aluminum Paste SilberlineManufacturing Co. 25.1 Cyclohexanone BASF Corp.. 5.3 Under-coat CarrierLiquid FASCAT 4102 ™ Atofina-ARKEMA Chemicals, 0.2 CatalystPhiladelphia, PA FASCAT 2003 ™ Atofina-ARKEMA Chemicals, 0.6 CatalystPhiladelphia, PA Dibutyl Ether (DBE) Dow Chemical Co. 5 Under-coatCarrier Liquid Midland, MI Aromatic 100 Solvent Exxon-Mobil Chemical Co.52.2 Under-coat Carrier Liquid Houston, TX Diisobutylketone Dow ChemicalCo. 31.0 Under-coat Carrier Liquid Midland, MI

As shown in Table V, dibutyl ether (DBE), Aromatic 100 solvent™ andglycol ether EB™ were added to a mixing vessel. UCAR VMCA™ solutionvinyl (co)polymer was then added to the mixing vessel and stirred untilall of the (co)polymer was dissolved. Vestanat B 1358™ 2-butanoneoxime-blocked isocyanate under-coat cross-linker and Dynapol L 952™polyester (co)polymer having low number average functionality were thenadded the mixing vessel and mixed until the (co)polymer components weredissolved.

In a separate container, aromatic 100 solvent and A-2291FG aluminumflake paste were pre-mixed until a smooth consistency was obtained, thenthe pigment dispersion was added to the mixing vessel with additionalmixing. Two catalysts, FASCAT 4102™ and FASCAT 2003™ were added tocyclohexanone in a separate container, mixed until homogenous, thenadded to the mixing vessel with additional mixing. Dibutyl Ether (DBE),Aromatic 100 solvent and diisobutylketone were then added to the mixingvessel, and the under-coat coating composition was mixed untilsubstantially homogenous.

In Example 14, exemplary (a) under-coat coating compositions containing(i) a polyester (co)polymer blend, and (ii) an (phenolic) under-coatcross-linker, was prepared using the materials included in Table VIbelow and according to the methods described below.

TABLE VI Preparation of Exemplary Under-coat Coating Composition RawMaterial Example 14 Example 15 Raw Material Available From (% w/w) (%w/w) DOWANOL ™ PM Acetate Dow Oxygenated Solvents, 16.31 16.31Under-coat Midland, MI Carrier Liquid Xylene Sigma-Aldrich Chemical 8.108.10 Under-coat Co., Carrier Liquid St. Louis, MO Polyester (Co)polymerExample 1 10.02 0.00 Polyester (Co)polymer Example 2 52.22 0.00 URALACZW5007SH DSM Resins U.S., Inc., 0.00 62.24 Polyester (Co)polymerAugusta, GA BAKELITE PF 6470 LB ™ BAKELITE ™, A.G., 8.90 8.90 ResolePhenolic Resin @ Iserlohn, Germany 76% w/w in n-Butanol VARCUM 2227B55 ™ Reichhold Chemical A.G. 3.95 0.00 Resole Phenolic Resin @ Austria55% w/w in n-Butanol BAKELITE 9989LB ™ BAKELITE ™, A.G., 0.00 3.95Resole Phenolic Resin Iserlohn, Germany CYCAT 600 ™ Cytec SurfaceSpecialties, 0.06 0.06 Catalyst West Paterson, NJ DOWANOL PM ™ DowOxygenated Solvents, 0.24 0.24 Under-coat Midland, MI Carrier LiquidADDITOL XK406 ™ Cytec Surface Specialties, 0.20 0.20 Catalyst WestPaterson, NJ

As shown above in Table VI, a blend of two synthetic polyester(co)polymers from Examples 1 and 2, prepared at a weight ratio of about1/5, was added to a substantially nonaqueous solvent mixture of DOWANOL™PM Acetate and xylene in a mixing vessel with external agitation. Thetwo hydroxyl-functional polyester resins exhibited a hydroxyl number of25 and 39 mg KOH per gram of resin, respectively.

Two resole phenolic cross-linking resins, Bakelite PF 6470 LB™ andVARCUM 2227 B55™, were supplied pre-dissolved in n-butanol and wereadded to the mixing vessel with external agitation. CYCAT 600™ catalystpre-dissolved in DOWANOL™ PM Acetate at about 20% w/w was then added tothe mixing vessel, followed by the addition of ADDITOL XL406™ catalyst.

In Example 15, a preferred variation of Example 14, a singlecommercially available polyester (co)polymer, URALAC ZW5007SH™, wassubstituted for the blend of two synthetic polyester (co)polymers fromExamples 1 and 2. In addition, a resole phenolic cross-linker, BAKELITE9989LB™, was substituted for VARCUM 2227 B55™ solution. The abovedescribed under-coat mixture was mixed until a substantiallyhomogeneous, free-flowing coating solution was obtained. This under-coatcomposition was used to coat metal substrates for use in fabricatingmetal scrolls. The percentages given in Table VI are standardized to100.

Example 16-18 Preparation of Exemplary Over-Coat Coating Compositions

In Examples 16-17, exemplary over-coat coating compositions containing apoly(vinyl chloride) (co)polymer dispersed in a substantially nonaqueousover-coat carrier liquid, an over-coat (phenolic) cross-linker, and anoxirane-functional (meth)acrylic (co)polymer, were prepared using thematerials and according to the formulation summarized in Table VII. Theweights presented in Table VII are in grams, and correspond to theweights of raw materials required to produce a 500 g batch of theunder-coat composition.

In Example 16, glycol ether EB™ and diisobutylketone were added to amixing vessel. UCAR VMCA™ solution vinyl (co)polymer was then added tothe mixing vessel and stirred until all of the (co)polymer wasdissolved. Geon 178198 PVC (co)polymer was added to the mixing vesseland dispersed at high speed for approximately 30 minutes, maintainingthe temperature between 29-35° C. The oxirane-functional (meth)acrylic(co)polymer of Example 11 and SANTOLINK EP 560™, a phenol-formaldehydeover-coat cross-linker were added to the mixing vessel with additionalmixing. Glycol ether EB™, Aromatic 100 solvent, 10% phosphoric acid in2- propanol (catalyst), and Lanco Glidd 4518V™ synthetic wax dispersionwere then added to the mixing vessel, and the over-coat coatingcomposition was mixed until uniform.

In Example 17, Glycol ether EB™ and diisobutylketone were added to amixing vessel. UCAR VMCA™ solution vinyl (co)polymer was then added tothe mixing vessel and stirred until all of the (co)polymer wasdissolved. Geon 178™ PVC (co)polymer was added to the mixing vessel anddispersed at high speed for approximately 30 minutes, maintaining thetemperature between 29-35° C.

TABLE VII Preparation of Over-coat Coating Composition Raw MaterialExample Example Raw Material Available From 16 (g) 17 (g) Glycol EtherEB ™ Dow Oxygenated 30.0 26.0 Over-coat Carrier Liquid Solvents,Midland, MI Diisobutylketone Dow Chemical Co. 65.0 55.5 Over-coatCarrier Liquid Midland, MI UCAR VMCA ™ Dow Chemical Co. 14.5 12.5 Vinyl(co)polymer Midland, MI GEON 178 ™ PolyOne Corp. 230.5 197.5 PVC(co)polymer Pasadena, TX Aromatic 100 Solvent Exxon-Mobil 0 35.5Over-coat Carrier Liquid Chemical Co. Houston, TX A-2291FG AluminumSilberline 0 35.5 Paste Manufacturing Co. Oxirane-functional Example 1279.0 67.5 GMA-(meth)acrylic copolymer SANTOLINK EP 560 ™ CYTEC Surface32.5 28.0 Phenol-formaldehyde Specialties, Basic-functional Over- WestPaterson, NJ coat Cross-linker Glycol Ether EB ™ Dow Oxygenated 12.511.0 Over-coat Carrier Liquid Solvents, Midland, MI Aromatic 100 SolventExxon-Mobil 12.5 11.0 Over-coat Carrier Liquid Chemical Co. Houston, TX10% Solution of The Valspar, Corp. 15.5 13.5 Phosphoric Acid Pittsburg,PA in 2-propanol Lanco Glidd 4518V Lubrizol, Corp. 8.0 6.5 Synthetic WaxWickliffe, OH Dispersion

In a separate container, aromatic 100 solvent and A-2291FG aluminumflake paste were pre-mixed until a smooth consistency was obtained, thenthe pigment dispersion was added to the mixing vessel with additionalmixing. A glycidyl methacrylate (GMA) oxirane-functional acrylic(co)polymer and SANTOLINK EP 560™, a phenol-formaldehydebasic-functional over-coat cross-linker were added to the mixing vesselwith additional mixing. Glycol ether EB™, Aromatic 100 solvent, 10%phosphoric acid in 2-propanol (catalyst), and Lanco Glidd 4518V™synthetic wax dispersion were then added to the mixing vessel, and theover-coat coating composition was mixed until uniform.

In Example 18, an exemplary over-coat coating composition containing apoly(vinyl chloride) resin dispersed in a substantially nonaqueousover-coat carrier liquid, an over-coat (phenolic) cross-linker, and acarboxyl-functional (meth)acrylic (co)polymer, was prepared using thematerials and according to the formulation summarized in Table VIII. Thepercentages given in Table VIII are standardized to 100 percent on aweight basis. The raw materials were charged to the mixing vessel in theorder listed in Table VIII. Lanolin was added to an agitated mixingvessel containing Aromatic Solvent 100 KB91™, Aromatic Solvent European(EU)™, DOWANOL™ PM Acetate and glycol ether EB™. The carboxyl-functional(meth)acrylic (co)polymer of Example 7 was then added to the mixingvessel with additional agitation. GEON 178™ PVC homopolymer was thenadded to the vessel and mixed with a high speed disperser forapproximately 60 minutes at 30-35° C. to obtain a substantiallyhomogenous PVC dispersion, taking care not to exceed a temperature of35° C.

Two resole phenolic cross-linking resins, VARCUM 2227 B55™ and DUREZ33163™, were then added to the mixing vessel with additional agitation.LUBA-PRINT 887/C™ Wax Dispersion was then added with additional mixing,followed by TINSTAB

OTS 17 MS™ hydrogen chloride scavenger in a mixture of xylene and ethylacetate. After additional mixing, aluminum sec-butoxide catalyst wasadded to the mixture, followed by additional mixing. The over-coatmixture of Example 8 was mixed until a macroscopically homogeneous,free-flowing coating dispersion was obtained.

TABLE VIII Preparation of Exemplary Over-coat Coating Composition RawMaterial Raw Material Available From Example 18 (% w/w) Aromatic Solvent100 KB91 ™ Exxon/Mobil Chemical Co., 7.35 Over-coat Carrier LiquidHouston, TX Aromatic Solvent 100 EU ™ Exxon/Mobil Chemical Co., 1.89Over-coat Carrier Liquid Machelen, Belgium Glycol Ether EB ™ DowOxygenated Solvents, Inc., 7.88 Over-coat Carrier Liquid Midland, MIDOWANOL PM Acetate ™ Dow Oxygenated Solvents, Inc., 8.42 Over-coatCarrier Liquid Midland, MI Lanolin Sigma-Aldrich Chemical Co., 0.63 St.Louis, MO Carboxyl-functional Example 7 11.79 (meth)acrylic CopolymerGEON 178 ™ PolyOne Corp., 40.39 PVC Homopolymer Pasadena, TX VARCUM 2227B 55 ™ Reichhold Chemical A.G. 5.69 Resole Phenolic Resin Austria DUREZ33163 ™ DUREZ Corp, 11.06 Resole Phenolic Resin Dallas, TX LUBA-PRINT887/C ™ L. P. Bader & Co., GmbH, 1.28 Wax Dispersion/Lubricant Rottweil,Germany Xylene Sigma-Aldrich Chemical Co., 1.44 Over-coat Carrier LiquidSt. Louis, MO Ethyl Acetate ™ Sigma-Aldrich Chemical Co., 0.51 Over-coatCarrier Liquid St. Louis, MO TINSTAB OTS 17 MS ™ AKZO-Nobel Chemicals,Inc., 1.05 Hydrogen Chloride Scavenger Chicago, IL Aluminum sec-ButoxideAKZO-Nobel Chemicals, Inc., 0.62 Catalyst Chicago, IL

Example 19-22 Substrates Coated With Inventive Coating Compositions

To demonstrate the usefulness of a coating composition of the presentinvention, an exemplary two-coat BPA, BPF, BADGE and BFDGE-free coatingcomposition described above was applied to sheets of tin-plated steel(electro-plated tin plate, ETP).

In Example 19, the under-coat of Example 13 was applied to the metalsubstrate using a #12 wire-wound applicator rod at a targeted curedcoating weight of 6.2 g/m², then baked (stoved) for ten minutes at about204° C. to effect curing. The over-coat of Example 16 was then appliedto the cured under-coated metal substrate using a #14 wire-woundapplicator rod at a targeted cured coating weight of 11.6 g/m², thenbaked (stoved) for ten minutes at about 204° C. to effect curing.

In Example 20, the under-coat of Example 13 was applied to the metalsubstrate using a #12 wire-wound applicator rod at a targeted curedcoating weight of 6.4 g/m², then baked (stoved) for ten minutes at about204° C. to effect curing. The over-coat of Example 17 was then appliedto the cured under-coated metal substrate using a #14 wire-woundapplicator rod at a targeted cured coating weight of 11.6 g/m², thenbaked (stoved) for ten minutes at about 204° C. to effect curing.

The cured coated sheets from Examples 19 and 20 were then evaluated forflexibility by stamping 206 easy-open food can ends and by drawing202×200 food cans.

In Example 21, the exemplary blended two polyester (co)polymerunder-coat coating composition of Example 14 was applied as a base-coator primer to electrolytic tin plate (ETP) scrolled sheets in an amountsufficient to provide about 7 g/m² on a dry weight basis, then stoved(cured) for about ten minutes (oven dwell time) at an oven temperatureof about 200° C. (peak oven temperature) for about 12 minutes (ovendwell time) to provide an adherent, cross-linked, cured over-coatcomposition on the under-coat composition covering the metal substrate.The exemplary over-coat coating composition of Example 18 was thenapplied as a top-coat or lacquer over the cured under-coat primer layerat approximately 14 g/m² (dry film weight) and baked at an oventemperature of about 190° C. (peak oven temperature) for about tenminutes (oven dwell time). The coated and cured multi-coat scrolledsheets of Example 21 were processed into 65 mm diameter “easy-open” endclosures.

In Example 22, the exemplary single polyester resin under-coat coatingcomposition of Example 15 was applied as a base-coat or primer totin-free steel (TFS) scrolled sheets in an amount sufficient to provide8 g/m² (dry film weight) of cured coating composition on the scrolledsurface, then stoved for about 12 minutes (oven dwell time) at about200° C. (peak oven temperature) to provide an adherent, cross-linked,cured coating composition on the metal substrate. The exemplaryover-coat coating composition of Example 18 was then applied as atop-coat or lacquer over the cured under-coat primer layer atapproximately 12 g/m² (dry film weight) and baked at an oven temperatureof about 190° C. (peak oven temperature) for about ten minutes (ovendwell time). The coated and cured multi-coat scrolled sheets wereprocessed into 83 mm diameter “easy-open” end closures.

(Comparative) Example 23-25 Substrates Coated With Control Compositions

Example 23 is a commercial two-coat epoxy-based “gold lacquer”composition that includes an under-coat primer containing a combinationof an epoxy (co)polymer and a phenolic (co)polymer and a top-coatlacquer containing a combination of a polyvinyl chloride organosol, aphenolic (co)polymer and a NOGE/epoxidized linseed oil (ELO) PVCstabilizer (available from the Valspar Corp., Pittsburgh, Pa.). Thecontrol gold lacquer composition of Example 23 was applied toelectrolytic tin plate (ETP) scrolled sheets at approximately 6.2 g/m²for the under-coat and 11.6 g/m² for the over-coat.

Examples 24-25 tare two different commercially available three-coatepoxy “gold lacquer” control compositions prepared using an under-coatprimer containing a combination of an epoxy resin and a phenolic resinand two layers of a top-coat lacquer containing a combination of apolyvinyl chloride organosol, a phenolic resin and a NOGE/epoxidizedsoybean oil (ESBO) stabilizer. The under-coat primer of each of Examples24-25 was applied at approximately 4-5 g/m², and the over-coat lacquerwas applied in two passes at approximately 12 g/m² per pass (Example 24)or 8 g/m² per pass (Example 25). The control compositions of Examples24-25 were applied to electrolytic tin plate scrolled sheets and stovedto provide a cured protective coating used for fabricating food storagecontainers and 65 mm diameter “easy-open” end closures.

Evaluation of Metal Substrates Coated With Coating Compositions

The inventive multi-coat system coated metal substrates were tested,comparatively to the control compositions of Examples 23-25, for use infabricating foodstuffs storage containers and particularly metalclosures for food or beverage containers. In addition to the extent ofcure of the coatings and their visual aesthetic appearance when coatedon the metal substrates, other important characteristics of the curedcoating compositions of the present invention preferably include: (1)providing a coating capable of adhering to the metal substrate, (2)providing a coating that exhibits excellent flexibility, and (3)enhancing corrosion inhibition of the metal substrate, particularlyunder sterilization or pasteurization conditions.

Accordingly, the cured coatings of Examples 19-25 were tested foradhesion to the metal substrate, for flexibility, for ability to inhibitcorrosion of the metal substrate and for chemical resistance to modelfoodstuffs and sterilization conditions. The following test methods areoffered to aid in understanding of the present invention and are not tobe construed as limiting the scope thereof. The coated composite metalsubstrates and multi-part food container components described above wereevaluated by tests as follows:

Cured Film Performance Coating Uniformity/Porosity

This test method determines the amount of metal substrate surface thathas not been effectively coated by the protective coating. The extent ofmetal exposure for metal substrates (e.g. cans or ends) was determinedusing a WACO enamel rater (Wilkens-Anderson Co., Chicago, Ill.) in4-second mode using an electrolyte solution consisting of 989.7 gramsdeionized water, 10 g sodium chloride (NaCl) and 0.3 g Aerosol OT-B(available from CYTEC Industries, West Paterson, N.J.).

If any uncoated metal is present on the surface of the metal substrate,then a current is passed between these two probes and registers as avalue on an LED display. The LED displays the conveyed currents inmilliamps, or more commonly referred to as ‘mAs’. The current that ispassed is directly proportional to the amount of metal that has not beeneffectively covered with coating. The goal is to achieve 100% coatingcoverage on the metal substrate, which would result in an LED reading of0.0 mAs.

Cross-Hatch Adhesion

To assess adhesion, cans and can end closures were subjected to avariety of tests to determine the adhesion of the coating to the metalsubstrate, including, for example, the cross hatch adhesion test.

For Examples 19-20 and Comparative Example 23 only, cross-hatch adhesiontests were performed according to ASTM Test Method D 3359—Test Method B.In the cross-hatch adhesion test, the headspace region of the can or thecan end is ‘cross-hatched’ in a ‘tic tac toe-like’ pattern with a sharpobject. Once this crosshatch pattern is made this region is investigatedwith Scotch® #610 tape (3M Company, St. Paul. Minn.) to assess theability of the coating to maintain adhesion in this area. The adhesionrating scale is 0-10, with ‘10’ meaning that 100% of the coating in thisarea has maintained adhesion, a ‘9’ meaning that 90% of the coatingremains in the tested area, and so on. A ‘0’ is assigned when 100% ofthe coating in this region is removed by the tape. The adhesion ratingreported is an average rating for three cans or three can ends.

For Example 21 and Comparative Example 24 only, cross-hatch adhesiontests were performed generally according to ASTM Test Method D 3359—TestMethod B. However, the adhesion rating scale for these two examples is“A-E”, with ‘A’ meaning that 100% of the coating in this area hasmaintained adhesion, and “E” meaning that 100% of the coating has beenremoved from the tested area, and so on. A “+” or “−” indicatorindicates a rating intermediate between to ratings. Thus, an “A−” and“B+” rating are equivalent, and indicate a rating between “A” and “B”,and so on.

Cured Film Corrosion Resistance

To evaluate corrosion resistance of the cured films, cans and can endswere sterilized against various food simulants for about 60 minutes at121° C. and 15 pounds per square inch (about 1 atmosphere) pressureunless stated otherwise. These food simulants include:

Tap water;

Deionized water;

1 and 2% w/w lactic acid in deionized water;

1 and 3% w/w NaCl in tap water;

2% w/w citric acid in tap water;

1% w/w citric acid/1% w/w NaCl in tap water;

1.5% w/w lactic acid/2% w/w NaCl in tap water;

1, 2 and 3% w/w NaCl/citric/lactic acid in tap water;

3% w/w acetic acid

3% w/w acetic acid/2% w/w NaCl

Peas (250 grams (g) frozen peas, 0.5 g cysteine hydrochloridemonohydrate, 0.25 g sodium carbonate, and 500 g water)

Peas were pre-heated to 71° C. prior to the filling and closure of thecan. After retorting, the container and its contents were then frozen.

Coating Test Results Coated Metal Food Cans

As shown in Table IX, the inventive BPA, BPF, BADGE and BFDGE-freetwo-coat coating compositions of Examples 19-20, when applied as a thinprotective coating, were of comparable performance to the commercialtwo-coat “gold lacquer” controls coatings of Example 23 with respect toflexibility and with respect to adhesion and flexibility aftersterilization. The commercial “gold lacquer” uses an epoxy-basedunder-coat and a PVC-based over-coat. All coatings in Table IX wereprepared at the same dried film coating weights.

As demonstrated in Table IX, a coating composition of the presentinvention, after curing, exhibited comparable chemical and corrosionresistance when compared to the commercial two-coat epoxy “goldlacquer.” The exemplary inventive coating composition also provides acured coating composition that exhibits excellent flexibility.Flexibility is an important property of a cured coating compositionbecause the metal substrate is typically coated with the protectivecoating prior to stamping or otherwise shaping the metal substrate intoa desired metal article, such as a metal container or a metal endclosure for a multi-part metal foodstuffs storage container.

The coated metal substrate undergoes severe deformations during theshaping process, and if a cured coating composition lacks sufficientflexibility, the coating can form cracks, or fractures. Such cracksresult in corrosion of the metal substrate because the aqueous contentsof the container have greater access to the metal substrate. Inaddition, a cured coating composition provided by a composition of thepresent invention is sufficiently adhered to the substrate duringprocessing into a metal article, thereby further enhancingprocessability and corrosion inhibition.

TABLE IX Evaluation of Coated Metal Food Cans (202 × 202) Example 19(Non- Example 20 Example 23 TEST Pigmented) (Pigmented) (Comparative)Under-coat Composition Example 13 Example 13 Epoxy-phenolic Dry CoatingWeight (g/m²)  6.2  6.4  6.2 Over-coat Composition Example 16 Example 17PVC-phenolic- NOGE/ELO Dry Coating Weight (g/m²) 11.6 11.6 11.6 InitialDry Adhesion 10 10 10 Metal Exposure (mA)  0  1  1 After Deionized WaterRetort Adhesion 10 10 10 Metal Exposure (mA)  0  1  1 Blush None NoneNone Corrosion/Blisters None None None After Lactic Acid Retort Adhesion10 10 10 Metal Exposure (mA)  1  1  1 Blush None Slight SlightCorrosion/Blisters None None Slight After Salt/Acetic Acid RetortAdhesion 10 10 10 Metal Exposure (mA)  2  2  2 Blush None Slight SlightCorrosion/Blisters None None Moderate

Coated Metal Scrolls

The present invention also provides a method of coating the multi-coatBPA, BPF, BADGE and BFDGE-free coating composition to a metal substratesuch as a metal scroll used in a coil coating process. The exemplaryinventive two-coat composition of Example 21 was applied in a two-passroll coating operation to electrolytic tin plate at a rate of 15-23grams of total cured coating composition per square meter of coatedsubstrate surface (i.e. application of 6-8 g/m² of the under-coatcomposition coated on the metal substrate as a primer, followed bystoving of the under-coat composition, followed by application of 9-15g/m² of the over-coat composition coated on the cured under-coatcomposition on the metal substrate, followed by stoving of themulti-coat system). Stoving was effected at a time and temperaturesufficient to provide an adherent, cross-linked multi-coat protectivecoating, generally 7-15 minutes at 180-210° C.

As shown in Table X, the inventive BPA, BPF, BADGE and BFDGE-freetwo-coat coating compositions of Example 21 are equivalent inperformance to the three-coat epoxy-based “gold lacquer” controlcoatings of Example 24 with respect to porosity, cross-hatch adhesionand appearance after sterilization. The inventive coating system mayalso be sufficiently well-adhered to the metal substrate to facilitateprocessing of the coated metal scroll into a metal foodstuffs containerwithout delamination or failure of the coating, thereby enhancingprocessability and corrosion resistance.

The inventive BPA, BPF, BADGE and BFDGE-free two-coat coatingcomposition of Example 21 is superior in performance with respect tostorage of simulated acidic foodstuffs when compared to the comparativethree-coat epoxy gold lacquer control. The present coating compositionspass cross-hatch adhesion tests in a variety of chemical environmentssimulating exposure to foodstuffs, and performs particularly wellcompared to the comparative commercial gold lacquers, particularly underacidic conditions. Thus, the exemplary inventive two-layer coatingcompositions may provide superior citric acid, lactic acid and aceticacid resistance over the corresponding three-layer gold lacquer control.

TABLE X Evaluation of Coated 65 mm ETP Easy Open End Closures Example 24Example 21 (Comparative TEST (Two-Coat) Three-Coat) Under-coatComposition Example 14 Epoxy-phenolic Dry Coating Weight (g/m²)  8 4-5Over-coat Composition Example 18 PVC-phenolic- NOGE/ESBO Dry CoatingWeight (g/m²) 12 12 Third-coat Composition N/A Same as Over-coat DryCoating Weight (g/m²) N/A 12 Coating Uniformity Initial Porosity Beforeretort 1.3 mA 2.5 mA After retort in 3% salt 2.6 mA 2.9 mA Porosityafter Added Cure (10 minutes @ 200° C.) Before retort 1.8 mA 0.5 mAAfter retort in 3% salt 1.6 mA 1.6 mA *Headspace Corrosion- resistanceBlush/Cross-hatch Adhesion Strong Blush/A− Strong Blush/A Tap water OK/BSlight Blush/A 3% NaCl in water OK/A OK/D− NaCl/citric/lactic acid OK/ARough/C+ NaCl/acetic acid Blush, Slight Strong Blush, Frozen peasStain/A− Stain/A *Easy open end closures were sealed to an upright canfilled with the indicated test substance.

The exemplary inventive coating composition also preferably provides acured coating composition that exhibits excellent flexibility.Flexibility is an important property of a cured coating compositionbecause the metal substrate is typically coated with the protectivecoating prior to stamping or otherwise shaping the metal substrate intoa desired metal article.

The coated metal substrate undergoes severe deformations during theshaping process, and if a cured coating composition lacks sufficientflexibility, the coating can form cracks, or fractures. Such cracksresult in corrosion of the metal substrate because the aqueous contentsof the container or bottle have greater access to the metal substrate.

The above-described advantages make a coating composition of the presentinvention useful for application on the interior surface of a variety ofmetal articles, such as for the interior of vacuum-packed metalcontainers. However, the present coating composition may also be useful,after curing, as a corrosion-inhibiting coating on “easy-open” metal endclosures for multi-part foodstuffs storage containers, particularlycontainers for vacuum-packed foodstuffs.

Easy-Open End Closures

The exemplary inventive compositions of Examples 19, 20 and 22 wereevaluated on tinplate for use on easy-open end closures. Easy-open endclosures require cured coatings exhibiting high flexibility andsterilization resistance, as well as processing performance that passesthe normal tests such as drawn can fabrication. The suitability of theexemplary inventive coating composition as a protective coating systemfor “easy-open” end closures for multi-part metal foodstuffs containerswas also evaluated.

“Easy-open” metal foodstuffs container end closures were fabricated bycoating either the exemplary inventive multi-coat coating system ofExample 22 or the control 3-coat “gold lacquer” of (Comparative) Example25 onto commercially available aluminum can end stock using a wire woundbar to obtain a dry coating thickness of 7.5 g/m². The coated panelswere then baked in a simulated coil line oven for 11 seconds to a peakmetal temperature of about 232° C. for approximately one second.

The exemplary inventive multi-coat coating system of Example 22 and thecontrol three-coat “gold lacquer” of (Comparative) Example 25 werecoated onto TFS panels and fabricated into metal closures. The closureswere subjected to accelerated corrosion testing as previously described;the test results are summarized in Table XI.

In addition, the inventive two-coat hardenable composition of Examples19 and 20, along with the comparative two-coat “gold lacquer” controlcompositions of (Comparative) Example 23, were coated onto tin platepanels and fabricated into “easy open” metal food closures as previouslydescribed. The closures were subjected to accelerated corrosion testingas previously described; the test results are summarized in Table XII.

Tables XI and XII show that the exemplary inventive two-coat compositionpassed fabrication of the closures, integrity requirements at elevatedtemperatures, and compound adhesion tests. In all tests, the inventivecomposition performed better than or equal to the control three-coatepoxy gold lacquer composition.

TABLE XI Evaluation of Coated 83 mm TFS Easy-open End Closures Example25 Example 22 (Comparative) Three- TEST Two-Coat Coat Under-coatComposition Example 14 Epoxy-phenolic Dry Coating Weight (g/m²)  8 4-5Over-coat Composition Example 18 PVC-phenolic- NOGE/ESBO Dry CoatingWeight (g/m²) 12 8 Third-coat Composition N/A Same as Over-coat DryCoating Weight (g/m²) N/A 8 Sterilization-resistance Porosity BeforeRetort 1.1 mA 0.2 mA After Sterilization (1 Hour @ 131° C.): Deionizedwater 0.5 mA 0.8 mA 1% NaCl 2.3 mA 1.0 mA 1% Citric acid/1% NaCl 2.1 mA1.4 mA 2% Citric acid 1.3 mA 3.4 mA 1.5% Lactic acid/2% NaCl 1.7 mA 3.2mA 2% Lactic acid 2.7 mA 1.6 mA 3% Acetic acid/2% NaCl 1.1 mA 2.5 mA 3%Acetic acid 1.4 mA 1.2 mA

TABLE XII Evaluation of Coated Metal Easy-open End Closures (206)Example 19 (Non- Example 20 Example 23 TEST Pigmented) (Pigmented)(Comparative) Under-coat Composition Example 13 Example 13Epoxy-phenolic Dry Coating Weight (g/m²)  6.2  6.4  6.2 Over-coatComposition Example 16 Example 17 PVC-phenolic- NOGE/ELO Dry CoatingWeight (g/m²) 11.6 11.6 11.6 Initial Dry Adhesion 10 10 10 MetalExposure (mA)  0  0  0 After Water Retort Adhesion 10 10 10 MetalExposure (mA)  0  1  1 Blush None None None Corrosion/Blisters None NoneNone After Lactic Acid Retort Adhesion 10 10 10 Metal Exposure (mA)  1 2  6 Blush None Slight Slight Corrosion/Blisters None None Slight AfterSalt/Acetic Acid Retort Adhesion 10 10 10 Metal Exposure (mA)  2  2  3Blush None Slight Slight Corrosion/Blisters None None Moderate

The above specification, examples and data provide a written descriptionof the BPA, BPF, BADGE and BFDGE-free, hardenable coating compositionsof the present invention, as well as the methods of making and methodsof using the metal substrate coating system to produce metal foodstuffsstorage containers according to the present invention. Various preferredembodiments of the invention were also described. These and otherembodiments of the invention reside within the scope of the followingclaims.

1. A hardenable packaging coating composition, comprising: an under-coatcomposition, containing: a polyester (co)polymer, and an under-coatcross-linker; and an over-coat composition, containing: a poly(vinylchloride) (co)polymer dispersed in a substantially nonaqueous over-coatcarrier liquid, an over-coat cross-linker, and a functional(meth)acrylic (co)polymer; wherein the packaging coating composition issubstantially free of mobile BPA, BPF, BADGE and BFDGE.
 2. Thehardenable packaging coating composition of claim 1, wherein theunder-coat composition further contains a substantially nonaqueousunder-coat carrier liquid.
 3. The hardenable packaging coatingcomposition of claim 1, wherein the over-coat composition is completelyfree of BPA, BPF, BADGE and BFDGE.
 4. The hardenable packaging coatingcomposition of claim 1, wherein the polyester (co)polymer exhibits ahydroxyl number from about one to about 40 milligrams KOH per gram. 5.The hardenable packaging coating composition of claim 1, wherein thepolyester (co)polymer exhibits a glass transition temperature of atleast about 50° C.
 6. The hardenable packaging coating composition ofclaim 1, wherein the polyester (co)polymer is present in an amount fromabout 20 to about 90 percent by weight of the under-coat coatingcomposition on a non-volatile solids basis.
 7. The hardenable packagingcoating composition of claim 1, wherein the under-coat cross-linkercontains two or more functional groups selected from hydroxyl, amino,vinyl and isocyanate groups.
 8. The hardenable packaging composition ofclaim 7, wherein the under-coat cross-linker is selected from the groupconsisting of phenoplast, aminoplast, and blocked isocyanatecross-linkers.
 9. The hardenable packaging coating composition of claim8, wherein the blocked isocyanate cross-linker has a blocking groupselected from 2-butanone oxime, ε-caprolactam and diethyl malonate; andthe isocyanate is selected from HDI, IPDI, TMXDI, H₁₂MDI and TMI. 10.The hardenable packaging coating composition of claim 1, wherein theunder-coat cross-linker is present in an amount from about 5 to about 30percent by weight of the under-coat composition on a non-volatile solidsbasis.
 11. The hardenable packaging coating composition of claim 1,wherein the poly(vinyl chloride) (co)polymer is dispersed in thesubstantially nonaqueous carrier liquid in an amount from about 60 toabout 85 percent by weight of the over-coat coating composition on anon-volatile solids basis.
 12. The hardenable packaging coatingcomposition of claim 1, wherein the over-coat cross-linker contains twoor more functional groups selected from hydroxyl, amino and isocyanategroups.
 13. The hardenable packaging coating composition of claim 1,wherein the over-coat cross-linker is present in an amount from about 5to about 30 percent by weight of the over-coat coating composition on anon-volatile solids basis.
 14. The hardenable packaging coatingcomposition of claim 1, wherein the functional (meth)acrylic (co)polymercontains at least one functional group selected from the groupconsisting of hydroxyl, carboxyl, and oxirane.
 15. The hardenablepackaging coating composition of claim 1, wherein at least one of theunder-coat and over-coat compositions further contains from about 0.1weight percent to about 5 weight percent of a catalyst on a non-volatilesolids basis.
 16. The hardenable packaging coating composition of claim1, wherein one or both of the under-coat and over-coat compositionsfurther contains at least one of a hydrogen chloride scavenger or apigment.
 17. The hardenable packaging coating composition of claim 16,wherein the hydrogen chloride scavenger is selected from monooctyl tinmercaptide, dioctyl tin mercaptide, dibutyl tin dilaurate and dibutyltin maleate; epoxidized linseed oil, epoxidized soy bean oil, dimer acidDGE and epoxidized polybutadiene; and the pigment is selected fromaluminum flake, titanium dioxide, and zinc oxide.
 18. A method ofcoating a metal substrate with a hardenable packaging system,comprising: applying an under-coat composition to a metal substrate,said under-coat composition containing: a polyester (co)polymer, and anunder-coat cross-linker; applying an over-coat composition to theunder-coated metal substrate, said over-coat composition containing: apoly(vinyl chloride) (co)polymer dispersed in a substantially nonaqueousover-coat carrier liquid, an over-coat cross-linker, and a functional(meth)acrylic (co)polymer; and curing the under-coat and over-coatcompositions to provide a hardened film of the under-coat and over-coatcompositions on the metal substrate; wherein the hardenable packagingcomposition and hardened film are substantially free of mobile BPA, BPF,BADGE and BFDGE.
 19. A metal foodstuffs container having at least aninterior surface coated with a hardened packaging composition producedaccording to the method of claim
 18. 20. A metal foodstuffs containeraccording to claim 19, wherein the metal foodstuffs container is amulti-part can having at least one easy-open end closure with at leastan interior surface of the easy-open end closure coated with a hardenedpackaging coating according to the method of claim 18.